 Welcome to the second module of managerial economics. In a previous 7 lectures, we are discussing about the introduction to managerial economics and then different tools and techniques that how generally the decision making is done and what is or what is being used for the decision making. So, our second module consists of theory of demand, which talks about demand analysis, essentially how demand is related with the other market forces like supply or how it leads to equilibrium and also we will talk about the different law of demand, whether that is in term of demand, consumer demand or in term of the utility. So, basically this module will talk about three topics. One is the demand analysis, second one is the elasticity of demand and third one is consumer behavior. So, if you will do a quick recap what we did in the last module, we introduced the subject managerial economics, how develop from that subject economics. Then we discuss about few concept that used in the business decision making. Then we discuss about the tools and technique for economic analysis and finally, we discuss about the optimization technique. Now, this present module the focus is on the demand, supply, the equilibrium, how the elasticity of demand and elasticity of supply generally takes place and finally, what is the consumer response to the change in the demand and change in the supply, what we will be discussing through the consumer behavior. So, if you look at the economy runs on its market and market works on certain market principle, there is a set of principle, there is a set of laws on that basis generally the market work. So, market works on a certain market principle and that governs the working of the market system. So, in other word generally we call that as the market mechanism and working of any market system, the basis always on the basis of the fundamental laws of the market and the fundamental laws of the market is nothing, but the law of demand and supply because demand and supply are the two market forces those essential for the working of the market system. So, when we talk about the fundamental laws of market, its laws of demand and laws of supply. So, in today's session we will focus more on the first part of the market forces that is demand forces. We will define the demand, we will discuss what is the law of demand, how it works, then we will discuss a demand schedule, how the demand curve is basically drawn, what is the demand function, what are the factors that affect demand and in which scenario there is a change or there is a shift in the demand. Then the second part of this session will be on second market forces that is supply forces. So, we will define what is supply, we will discuss the law of supply, then we will discuss the exception of law of supply in which scenario generally the law of supply never works out as per the rule or as per the principle. Then we will discuss about a supply schedule, we will talk about a supply curve, supply function, supply function keeping by two variable and the multivariable, then we will talk about the factors affecting the supply and in which scenario there is a change or the shift in the supply. And finally, looking at the demand forces and supply forces, we will see how the equilibrium is generally maintained in the economy or in the market, what are the preconditions in which cases when there is a change in the demand, when there is a change in the supply, how it leads to disturb the equilibrium, whether the equilibrium gets really disturbed or there is no change in the equilibrium, what are the scenarios that we are going to study in the market equilibrium. So, we will start from the first market force that is demand and when we define demand, this is basically a relation showing the quantity of the good that consumer are willing and able to buy at various prices per period or other things remaining constant. So, here if you look at the other things, whether it is the income, whether the market situation, whether it is the forecasting about the price, all other variables that has some say when it comes to demand for the product, all variables are remain constant and the relationship between the quantity of the goods or the quantity of the products and the maybe at a typical price or a typical time period that is generally demand. So, demand is nothing but a relation showing the quantity of a good that consumer are willing and able to buy at various prices per period, other things being constant. So, if you look at the definition, there are 2.1 is willing to buy and the other one is the able to buy the product. So, if you take forward this, then specifically a demand for commodity depends on 3 preconditions. The demand takes place when the consumer has the desire to acquire it, when the consumer has the willingness to pay for it and when it has the ability to pay for it. So, what is this desire to acquire it? Maybe there are many products, what the consumer is willing to pay for it or maybe he has the ability to pay for it, but till the time the consumer has no desire to acquire that product, we cannot convert that into demand because the consumer has to wish for the product, the consumer has to desire for that product, then only it can be converted into demand. The second criteria or the second precondition is willingness to pay for it. So, if you look at even if the consumer has a desire to pay for it, a desire to acquire the product, he has the ability to pay for it, if there is no willingness to pay for it, it cannot be again part of demand because the consumer is not ready to pay for the product. In that case, we cannot convert that into demand. Similarly, ability to pay for it, this is strictly on the basis of income, whether there is a purchasing power of the consumer is present or not. If there is a purchasing power is present in the consumer, then the consumer has also the ability to pay for it. So, in this case, if you look at the preconditions are three, desire to acquire it, willingness to pay for it and ability to pay for it. So, whether you if one of these three conditions or one of these preconditions are not being made, then in the demand is not possible. Even if the consumer has the willingness to pay for it, ability to pay for it, if the consumer has no desire to acquire it, it cannot be converted into or the part of demand. If the consumer has no willingness to pay for it, then again it cannot be part of demand. And if the consumer has no capability in term of money, in term of payment or may be not able to pay for the product, then again it cannot be considered as a demand. So, demand for commodity implies that the consumer has to consumer has the desire to acquire it, willingness to pay for it and the ability to pay for it. Then there are different types of demand. So, we will see few different types of demand. The first one is individual and market demand. The quantity of a commodity an individual is willing and able to purchase at a particular price during specific time period given his or her money income, taste and prices of the other commodity such as substitute, complete what is referred to as the individual demand for the commodity. So, individual to in a very simplified manner, individual demand is nothing but what the individual is willing to and able to purchase at a particular price. Any specific time period keeping his taste, keeping his price and also looking at what are the substitute and complements products available in the market. So, any consumer any specific time period at different price level or the same price level whatever the willingness to and ability to pay for it that is typically the individual demand. So, here we have introduced there are two term over here what needs may be little bit explanation. One is substitute and second is complements. So, one category is generally the substitute good another category is the complement goods. You take the example of tea and coffee. They are the substitute goods because if you look at people if they are not very specific about tea or not very specific about coffee, they consume these two products interchangeably. Either they have coffee or they have the tea. So, tea and coffee when one product is substitute of another product this is generally known as the substitute goods. Similarly, if you look at petrol or diesel, again it is the case of your substitute goods because one good is substitute for the other one. Similarly, complement is one where one product cannot be consumed without another product. So, if you take the case of again tea sugar or coffee sugar or tea milk or coffee milk again they are the complementary products because you cannot consume one product without the another. You take the example of suppose car petrol or car diesel you cannot run the car without petrol or without diesel. So, in this case we can say that car petrol or car and diesel they are the complementary to each other. Similarly, if you are coming to the food item like if you take the example of bread and jam or bread and butter again they are the complementary goods because you can the consumer cannot consume one goods without consuming another. So, if the product is independent it is not depend the consumption of the product is not dependent on any other product basically this is the normal goods. Otherwise, we get another two category of goods one is substitute good the typical example is again tea and coffee and second one is the complementary goods in this case one goods cannot be consumed without consuming the other goods. The typical example we always take whether it is car petrol car diesel butters bread or jam and bread. Similarly, maybe there are numerous examples where we can say that one goods cannot be consumed without the another good. So, considering this typically in case of individual demand irrespective of the substitute goods complementary goods the prices of the goods or the taste and preference of the consumer at any specific time or any specific time period whatever the consumer demand of typical commodity that becomes the individual demand. Suppose, if you look at what is your grocery demand per month that is that becomes the quantity demanded of a specific consumer on a specific month corresponding the prices of the different items in the grocery basket. The second one is the market demand market demand is the total quantity which all the consumer of the commodity are willing and able to purchase at a given price per time unit given their money income their test prices of the other commodity is referred to the market demand for the commodity. So, in this case if you look at the other things remaining constant the price is constant the income is constant the taste at the of the consumer at that typical prices of the other commodity whether it is substitute whether this complements their constant and given all these the total quantity what all the consumer they are consuming in a specific time period that becomes the market demand. So, if you take a simple example maybe you can take a case of how much of cup of coffee you take during a day some total of all the quantity per day per month basis that is your monthly individual demand for cup of coffee. But when it comes to the coffee vendor for him it is always not the individual demand what consumer one is consuming or what consumer two is consuming for it is that monthly how much unit of coffee that vendor is selling that is the market demand. So, if the market price of coffee is 6 rupees and all the 6 rupees price whatever they are consuming in a month that becomes the market demand. So, here product is coffee price is fixed the consumer whatever they consume throughout the month. So, in a specific time period on a monthly basis price of the coffee given at 6 all the consumer whatever the amount of coffee they are consuming that consist of the market demand. So, in one way we can say individual demand in a specific time period in a specific price that becomes the market demand for the product. Let us go to the second types of demand that is firms demand and industry demand. The quantity of firms product that can be sold at a given price overtime is known as the demand for the firms product. And the sum of demand for the product of all the firm in the industry is referred to the market demand or the industry demand . So, it is if you look at again it is the case of same differences between the individual demand and the market demand. Now, what is the difference between the firm and the industry? Industry is some total of the number of firms. The firm also produce a same product and the industry as a whole they also produce the same product. So, the quantity of the product what is being demanded for from the firm or from the typical firm that is become the firms product. And what is the sum total of demand for all the firms across the industry that becomes the industry demand. So, again we can explain it using the same concept that the sum total of all the firms product at a given price at a given time period is consist of the market demand or industry demand for the product. Because if you look at firm is nothing but the maybe the part of the industry or industry is nothing but the sum total of all firms in the industry. So, here also again the difference between the firm and industry product is firm is the individual productive unit and industry is the sum total of all the firms they are producing the same product. The third type of demand is autonomous demand or the derived demand. So, autonomous demand or the direct demand for a commodity is depends on its own out of the natural desire to consumer possess a commodity. This type of demand is independent of the demand of the other commodity. So, autonomous demand is there is no forces that guides the demand to happen. It generally comes from the natural desire to consume or natural natural desire to own a commodity or own a product. However, if you look at the derived demand for commodity which arises from the demand of other commodity that is called as the parent product is called generally the derived demand. So, in this case the demand for this product generally comes from the demand for the other product. So, if you take specifically what is the need of agriculture or what is the need for land or what are the need for fertilizer. You need land, you need fertilizer, you need agricultural harvesting and this is always a derived demand because the those commodity has demanded due to demand for food. Why the agriculture being done? Because there is a demand for grains and demand for grain comes from the fact that there is a demand for the food and that leads to demand for grain, that leads to demand for land, that leads to demand for fertilizer and that leads to demand for agricultural tools. So, the basic difference between the autonomous demand and the derived demand is autonomous demand is independent it can just happen, it can just take place when the consumer has the desire to acquire it, willingness to pay for it or ability to pay for it. Whereas, derived demand is where it comes from the demand for the other product. So, if you can connect this to this, this may be also like a product which is not direct but rather this indirect demand or may be derived demand because the demand takes place for the another product which leads to take which leads to which leads to the demand for this typical product. So, autonomous is direct and derived demand is always comes from the demand for the other product. The next category of types of demand comes is demand for durable and the durable goods. Durable goods are those goods for which the total utility or usefulness is not existable in the short run. Such goods can be used repeatedly over a period of time. So, it is a kind of non-perishable goods which can be used again and again the consumption can be repeat and the utility or the usefulness of the product is not with for one time consumption. So, durable goods are those products has a specific life time and it is not in the short run. And the non-durable good is basically the perishable good. It depends largely on the consumer current prices, consumer income and fashion. It is also subject to frequent change. If you look at the demand for durable goods, may be it is a vehicle may be it is a house which if you look at and their usefulness or their utility never goes overnight or it is not the short run rather the use for the typical durable goods for long. Like if you take the example of a refrigerator if you take the example of a computer, if you take an example of a television, specifically their life time is not short, their life time is long. At least it goes for 5 year, 10 years, 15 years and sometime more than that. So, the demand for these goods are always different from the non-durable good. Durable good is one because where the utility or the usefulness of the goods goes along with the consumption. So, once the good gets consumed the utility usefulness goes with that. So, the demand pattern is there is a variation in the demand pattern between the durable good and the non-durable goods. Like when there is a change, when there is a need to change the durable goods, when you feel that you have already used it for 5 years, you have already used it for 5 years, you are getting a good maybe if you are getting a good exchange offer, if you are getting a good maybe discount, you always feel I have already used this product for more than 10 years, more than 15 years and if I am getting a good result value and some discount on the new value, then I am going for it. Or when the technology changes, when the fashion changes along with that the demand for the durable goods change, if you look at the earlier it was just a normal screen, then we came to the age of flat screen and then now it is a case of LED and SILDI. So, in this case the demand changes, when the when we get a new product, when in term of maybe the change in the technology, change in the appearance or the change on the as you hold the product, when there is a new product is being launched. But in case of non-durable good life, you take the example of which is short, maybe vegetable is the short, non-durable good life. What we use as the clothes, what we use daily, maybe it is a pen, maybe it is a notebook, it is maybe diary. What we change frequently, because the utility that goes with a very short span, whatever the usefulness of the product that goes, like if you take the example of a ball pen, till the time ink is there it is being used. So, it is may be 10 days, it is may be 20 days, it may be 1 month, it may be 30 days short. And we need to change it when there is a requirement, either when there is a change in the price, when there is a change in the fashion and when there is a change in the income. How it is related to change in the price, maybe if the current price gets changes, if we are getting something good at lower price, you always offer bit. And because this is also a low value product as compared to the durable goods. Similarly, if the demand patterns on the basis of fashion, we feel that this is outdated and I am not going to consume it anymore. In that case again, the demand comes over there, because there is a change in the fashion and nobody use the outdated product, rather everybody opt to use for the whatever comes new in the market. So, that is the reason the use of durable and non-durable goods generally different and that leads to demand pattern of, demand pattern of durable and the non-durable goods. The last category what we discuss on the types of demand is short term and the long term demand. So, short term demand refers to the demand for goods over a short period, whereas long term demand refers to the demand which exist over a long period of time. So, in this case again we can link this to our demand for durable and non-durable goods. Generally, durable goods are long term demand, because demand which exist over a long period of time and demand for the goods over a short period or maybe again you can link this, because if it is usefulness is less, maybe you use that and this is a short term demand, because your next demand is something else. But long term demand is again what you use on the daily basis, that is then that again you can link that way long run demand. Now, we will discuss what is law of demand as we discussed in the very beginning that the market forces governs by the demand forces on the basis of certain principle, on the basis of certain laws. So, in this case we will see what is the law of demand. So, law of demand the basis is the relationship between the price and quantity demanded and this is generally known as economic law that how the price and quantity they are related to each other. The quantity of the goods demanded per period relates inversely to the price other thing constant. So, law of demand says that there is a inverse relationship between the price and quantity demanded other things remaining constant and what are the other things here, the other things here is that the factors that those affects the quantity demanded for the product. So, keeping all other things remaining constant which affects the quantity demanded the quantity of goods inversely related to the price in a typical time period. So, law of demand says that there is a inverse relationship between the price and quantity demanded other things remaining constant. So, whenever there is a increase in the price quantity demanded supposed to decrease and whenever there is a decrease in the price the quantity demanded supposed to increase assuming all the goods are normal goods. So, law of demand says that there is a inverse relationship between the price and quantity demanded assuming all the goods are normal good and all other things are remaining constant. But in few cases there is if you find the law of demand does not hold good. There are few exceptions where law of demand cannot be practiced or the law of demand does not hold good. The one example is given goods. So, till the time we have introduced three type of goods if you look at one is normal goods. Second one is the substitute good and third one is complementary goods. So, these are different kind of good that is given goods sometime this is also known as the inferior good or you can say it a specific case of inferior good this is the given goods comes into picture. Now, what is a given goods a given good is one in which one which people paradoxically consume more as the price rise violating the law of demand. So, in case of given good law of demand does not hold good because once the price increases for this product generally people they consume more of it. But what is the what law of demand tells us law of demand tells us that whenever there is a increase in the price of the product generally the quantity demanded for that product decreases. So, in this case the the pattern is not such because whenever there is a increase in the price there is a increase in the quantity demanded also and that that is why we say that this is not a normal good this is a given good and in case of given good law of demand does not hold good. So, there is a so in the background there is a story to this given goods how given goods comes into picture and how the how the law of demand does not hold good in case of given goods. So, during Irish potato fine in 19th century potato where the consider as the given good and potato where the largest staple in the Irish state. So, as the price rose it had a large impact on income. People responded by cutting out on luxury goods such as meat and instead of bought more potato therefore as the price of potato increased so did the demand. So, if you look at what is the consumption basket of Irish during that time in 19th century the consumption basket or their food basket consist of potato, meat and vegetables. But being potato is the staple diet the composition of potato more in the food basket. Price increases for potato there is no change in the income of the consumer. So, in this case what the consumer they will do since potato is the staple diet they need to have the same quantity even if there is a increase in the price. So, in this case one consumer what they did they started cutting down their expenditure on meat and vegetable which is considered to be the superior in the food basket and they bought more potato because potato is staple diet even if price increases still they have to consume the same amount. So, the expenditure from the other superior items from the consumption basket being cut that is meat and vegetable and the same money is diverted into potato. And in this case the price of potato increase and also the demand because even a price is increasing still people they are buying more of it which is again a exception to law of demand where the whenever there is a price in the price increases that leads to decrease in the quantity demanded. So, this is one case in case of given goods the price increases and along with that the quantity demanded also increases and that leads to exception of the law of demand. The second one is the weblen effect and this generally introduce the concept of conspicuous consumption and the status shaking. If you look at in our daily life it also happened that if something is expensive we always feel that this is good because there is a perception that if there is increase in the increase in the price of it generally it has to be good whether it is a designer product whether it is jewelry whether it is say maybe designer accessories we always feel that if they are it has to be a good quality. So, consumer there they have the perception that if price has been charged premium then the quality is good and the product is good and this is generally known as weblen effect. So, in this case even if there is a increase in the price people they always feel that if there is a increase in the price I think there is a increase in the quality and they generally go for it and also this is considered as status shaking if the if the consumer is consumed some highly priced product it always leads to the status shaking and in this case again the law of demand is not applicable. So, what is the perception over here the more expensive these commodities become the higher their value as a status symbol and hence the greater the demand for them. So, if it is more expensive they feel that it is again the value of the status symbol and they feel that is a good quality attached to it and there is a greater demand for it. So, the amount demand of this commodity increase with an increase in their price and decrease in their decrease with the price. So, in this so typically for this type of product when there is a increase in the price that leads to increase in the quantity demanded and when there is a decrease in the price people they stop consuming this or they decrease in consumption assuming that since this is a lower price product there is no quality attached to it or there is no value or the status attached to it. So, this is about if you look at in this case typically this is the perception of the consumer that high value goods is better quality and it leads it links to also status whereas, the low value good even if it is may be good still the perception is that low value product since it is not on a higher segment it is always a it is always a inferior product as compared to other product and generally they decreases their consumption for it. So, in case of wavelength goods or in case of wavelength effect again the law of demand does not hold good and the price and quantity demanded is not related inversely. There are one more exception that is law of demand that is in case of prediction or may be expectation of change in the price of the commodity. So, if the price is going to increase if there is a expectation if there is a prediction that the price is going to increase people they buy more the demand increases and if the price is going to decrease in the future that leads to decrease the consumption at this moment. So, sometimes their prediction when there is a prediction the law of demand does not work there. So, if you look at before budget if you have seen people they predict or people they do a forecast that after budget the price of this going to increase the price of this going to decrease that leads to some disturbance in the decision making or some disturbance in the the consumer patents for the consumer demand patent for different goods. If the price is going to increase the consumer feel that let me buy more. So, even if the price is on a higher side still the consumer buys more and if the price is going to decrease the consumer even if the price remain constant still the consumer is consuming less assuming the fact that when the price is going on a lower side is going to consume more. Similarly, if you look at whether the prediction is related to durable goods or whether the prediction is non durable goods. The prediction works well the prediction works more in case of durable goods because you cannot you in case of durable goods you can postpone your consumption till the time you are getting a favorable price. But in case of non durable goods the prediction never work because this is only kind of necessity what we use in our daily life. So, we cannot postpone the consumption and in that case generally the prediction the role is a bit less and in case of durable goods this generally works and law of demand does not hold good. Similarly, in case of share market or stock market where the basis is speculation if the price of the share is increasing price of the stock is increasing there is a perception of the consumer that may be again it is going to increase and they are going to get more value if they are buying more. So, since the basis of stock market is speculation the law of demand does not hold good there and this is one more exception to law of demand. So, if you look at by principle of by economic principle there should be inverse relationship between price and quantity demanded and that is generally known as law of demand. But in case of few instances or in case of few type of products generally the law of demand does not hold good like in case of a given good or when the market is governed by prediction or some kind of market like stock market share market where the basis is speculation the law of demand does not hold good. There may be few more examples like in which case like when it comes to suppose necessity. What is if the consumption is necessity or if people like emergency if it is a life saving drugs again the law of demand does not hold good even if price is on a higher side since it is a part of necessity this is a life saving drug the consumer they are not changing the demand pattern like if you take a medicine every day as a precaution or as a part of treatment generally the consumer takes that even if there is a increase in the price. So, in case of few extremes again the law of demand does not hold good. Then we will talk about the demand schedule and the demand curve demand schedule is a table that shows the relationship between the price of the good and the quantity demanded and demand curve is a graph of the relationship between the price of the goods and the quantity demanded. So, if you look the relationship between the price and quantity demanded it is again on the basis of inverse there is inverse relationship between the price and quantity demanded. So, when you graphically plot this of price and quantity in a graph looking at their principle or how they are related, we generally take quantity on the x axis and price on the y axis. And we know that there is a inverse relationship between the price and quantity demanded. So, on that basis demand curve always slopes downward, because whenever there is a increase in the price that leads to decrease in the quantity demanded, whenever there is a decrease in the price that leads to increase in the quantity demanded. So, suppose we take point A, point B and point C and this point A is combination y 1, x 1, point B is combination y 2, x 2 and point C is combination y 3, x 3. x is our quantity and y is our price. So, if you look when the price is y 1, the quantity is x 1, when price is y 2, the quantity is x 2, why there is a increase in the quantity from x 1 to x 2, because there is a decrease in the price from y 1 to y 2. Similarly, when the price is y 3, the quantity is x 3, why there is a increase in the quantity from x 2 to x 3, because there is a decrease in the price from y 2 to y 3. So, price and quantity since both are in inversely related whenever there is a decrease in the price that leads to increase in the quantity demanded and in similar way again we can explain that when there is a increase in the price. Suppose initially the price is y 3 and quantity demanded is x 3. Now, price of y 3 price is increases from y 3 to y 2. If you look at the quantity will decrease from x 3 to x 2 and again if the price is increasing from y 2 to y 1 the quantity will again decrease from x 2 to x 1. So, price and quantity they are both inversely related whenever there is a increase in the price that leads to increase in the quantity demanded decrease in the quantity demanded and whenever there is a decrease in the price that leads to increase in the quantity demanded. And demand curve is always a downward sloping demand curve because both price and quantity they are inversely related to each other. The next we will see a demand schedule this basically turns the relationship between the price and quantity demanded. So, if you look at there are 5 points a b c d e and each come in each point gives a combination of both the price and quantity. So, at the point a like if you look at the graph again we can put this into graph suppose when the price is 15 quantity demanded is 8 and again when the price is 12 quantity demanded is 14 price is 9 quantity demanded is 20. So, if you plot this again in a graph taking the number rather than y 1 y 2 y 3 if you are putting 15 12 and 9 and in this case x 1 x 2 x 3 again if you can put 8 14 and 20 again it shows the same relationship that whenever there is a decrease in the price that leads to increase in the quantity demanded. And whenever there is a increase in the price that leads to decrease in the quantity demanded. So, the same relationship is again shown in case of your demand schedule if you look at and if you look at the trend over here the price is decreasing like 15 12 9 6 3 and correspondingly the quantity demanded is increasing because there is a decrease in the price. Again if you read it from the below you will find that if you are moving from point e to point a you will find that when the price is increasing that again leading to the decrease in the quantity demanded. Any individual point on demand curve or demand schedule shows the quantity demanded or the entire demands or the entire demand curve or schedule that shows the demand. Now, we will see what are the factors generally that influence the demand. We know that one that is already we have been discussing in last couple of minutes that price and quantity they are inversely related. So, apart from price what are the other factors that influence the demand. So, the first one is price of goods and services, second one is the income of the consumer. How income of the consumer is related to quantity demanded? If the income increases they are positively related if the income increases the people the demand more the consumer demand more for the product and the third factor what influence the demand is the price of related goods and services. Like we are taking the example of tea and coffee. If you are consuming if the price of coffee decreases obviously, the demand for quantity demanded for tea generally decreases because the consumer will move from tea to coffee because coffee is now a low cost product as compared to the tea. So, that is how the price of related goods like price of substitute good price of complement goods that also influence the demand for the product. So, one is price of the product second one is the income of the consumer, third one is the price of related goods and services. The related goods and services in question can be substitute good can be complementary good. So, price of substitute good price of complementary good also influence the demand for this typical good. Then the taste pattern of the consumer if the consumer has developed a taste for it if the consumer has consumer has liked the product if they are happy about the usefulness of the product they have developed a taste for it and if they have developed a taste for it they will always the prefer this product as compared to the other product which will again influence the demand for the product. So, taste pattern of the consumer is again a positive relationship with the demand if the taste pattern is good generally the demand for the product is also good. Then the expected future price of the product if the future price is going to increase the demand is going to demand is going to be more now because if they are postponing their consumption they are paying more in the future rather than whatever the price they are paying now. So, expected future price of the product again pays a important role when it comes to the demand for the product. Then the number of consumer in the market more consumer consuming the product the demand for the product is more and they are positively related the number of the consumer is positively related to the quantity demanded for the product. So, the demand for the product essentially dependent on all the six factors that is prices of goods and services, income of the consumer because that reflects the purchasing power of the consumer, price of related goods and services, taste pattern of the consumer, expected future price of the product and finally the number of consumers in the market they generally leads that what should be the demand for the product. Now, what is a demand function? So, mathematically when you when you analyze the relationship between the price and quantity demanded that through a demand function and demand function it shows a relationship between the price and quantity demanded represented as P and Q D when all other variables are remain constant. So, the relationship of price and quantity demanded into a mathematical function we generally call as the demand function. So, in this case suppose we assume that all other fixed all other variable are constant like income price of the related goods and services, future price, number of consumers all other variable are constant they are not influencing demand at this point of time. Demand function is specifically the mathematical relationship between the quantity demanded and price. So, if you look at Q D is a function of price. So, quantity demanded is dependent on the price and the slope of Q D and P it should be it must be negative because quantity demanded price they are negatively related they are inverse related if one is increasing the other one should be decreasing and if the other one should be decreasing then the one should be increasing. So, the slope of quantity demanded and price has to be negative and demand function essentially it is the mathematical relationship between the price and quantity demanded. So, if you take a simple example Q D is equal to 500 minus 5 P a typical example of the demand function. So, how do we interpret this typical demand function? Here if you look at all other variable are constant because we do not have the value for income we do not have the value of the prices of other goods, future prices, number of consumer, taste meter. So, we can we can say that the quantity demanded is only dependent on price. So, Q D is equal to 500 minus 5 P now how do we interpret this typical demand function? At 0 price demand is equal to 500 units means if the if you are getting the product at free the demand is 500 units because the consumer who requires the product their number is only 500 minus negative sign shows inverse relationship between the price and demand and 5 implies that each 1 rupee change in the price demand price demand changes by 5 unit because Q D is again it is a minus 5 P 500 minus 5 P. So, 500 gives us the value of the value of the intercept and minus 5 gives us the value of the slope. So, 5 implies that for each 1 rupee change in the price demand changes by 5 units, negative sign shows the inverse relationship between the price and demand and at 0 price demand is equal to 500 unit. Now, if we consider a generalized demand function demand is not only dependent on price rather it depends on all the factors as we discussed before few minutes that number of factors that decides the that influence the demand. So, taking all this variable Q D is a function of price of the goods donated by 5 M that is income P R that is price of the related goods T is the taste per 10 P is the expected future price of the product and N is the number of consumer. So, generalized demand function consider all the factors that influence the demand for the product that is P is the price of product, M is the income, P R is the price of related goods and services, T is the taste per 10 of the consumer, P is the expected price of the product future price of the product and N is the number of consumer. Then if you formulate a generalized demand function that Q D is equal to A which is the value of intercept plus B P plus C M plus D P R plus E T plus F P E and G N where B C D E F G are the slope parameters and the slope parameters measure effects on quantity demanded of changing one of the variable while holding the other constant. So, slope variable says that what how they are related that is typical variable how they are related with the quantity demanded and the sign of parameter shows how variable is related to quantity demanded. If it is positive sign there is a direct relationship between that variable and the quantity demanded and if it is negative sign then there is a inverse relationship between that variable and the quantity demanded. So, now if you will see all this variable and how they are related price is inverse related to quantity demanded and the slope that is B which is del Q D by del P is negative, M is the income direct for normal good and inverse for inferior goods. It means when the consumer increases the consumer money income increases the quantity demanded for the normal goods increases whereas, the quantity demanded for the inverse goods is inferior goods decreases because when income increases people always prefer to buy the superior goods what they can afford now. So, that is the reason the normal goods there is a increase in the quantity demanded for the normal goods and there is a decrease in the quantity demanded for the inferior good. Like when the income increases you prefer to buy your own vehicle rather than going by the public transport. So, in this case own vehicle is a normal good and in public transport is a inferior good. So, when the consumer money income increases the consumer prefer to spend more on the normal goods and less on the inferior good that leads to the fact that income increases that leads to increase quantity demanded for more for the normal goods and less for the less for the inferior good and that is the reason that relationship is direct between the income and the quantity demanded and the inverse for between the quantity demanded and the quantity demanded of inferior good and the income. Again the price of related goods it is direct for substitute inverse for complement. Now, take the example of tea and coffee. When the price of coffee increases quantity demanded of coffee decreases, but the quantity demanded of tea increases it means when there is a increase in the price of substitute good that leads to increase in the quantity demanded of this good. So, if tea being the normal good or the goods in typical goods in this context a price of coffee increases that leads to increase in the quantity demanded of tea and that is why there is a direct relationship between the price of related good and the substitute good. Whereas, in case of complementary goods how it works? Suppose complementary goods is tea and sugar, a price of tea is price of sugar is increasing obviously, the price of tea will also a price of sugar is increasing that leads to decrease in the quantity demanded of sugar and that also leads to decrease in the quantity demanded of tea or may be you can put it in a other way around that if the price of tea is increasing that leads to decrease in the quantity demanded of tea and also leads to decrease in the quantity demanded of sugar because when tea is not demanded there is no demand for sugar specifically in this context. So, there is a inverse relationship between the price of complementary goods and the quantity demanded of this typical goods. So, the consumer's pattern they are direct because if the consumer is liking the product the more demand is there for this typical product. So, the slope variable is again positive that is del Q D by del T which is positive more the consumer more like the product more is the quantity demanded for this product then the expected future price of the product is again directly related to the quantity demanded. If the price of the product is going to increase in the future quantity demanded is more now because the consumer prefer to buy more at this point because the price is going to increase in the future and if the price of expected price is going to decrease the consumer is again postpone all his consumption to the time period when the price is going to decrease. So, expected future price of the product is directly related to quantity demanded because if it is going to increase then quantity demanded is increasing if it is going to decrease then quantity demanded is decreasing. And the last factor which influence the quantity demanded is the number of consumer in the market. If the number of consumers are more the quantity demanded is going to be more because more they demand for this product and if it is less then generally the quantity demanded is less. And market demand is again if you remember the difference between the individual demand and the market demand. Market demand is the sum total of all individual demand at each possible price and graphically if you look at market demand is the summation of all individual demand curve horizontally and generally all demand curve is summed horizontally in order to get the market demand curve. So, there is a change in the demand curve either due to change in the quantity demanded or due to change in the demand. So, demand changes either when there is a change in the price or when there is change in the all other factors that influence the quantity demanded for the product.