 In this video, we're going to talk about attracting real numbers using applications. This first example is asking us for the hourly change in temperature. If you look at this from 4 o'clock to 5 o'clock, we went from 82 degrees to 84 degrees. And most of us can look at that and say, oh, well, it went up 2 degrees. But how would we figure that using addition and subtraction? Well, to do that, we want to take the latest and then to track from the earliest temperature and see what we get. And if we take 84 minus 82, we see that it is a 2 degree difference. So we do the same thing for the rest of this table. From 5 o'clock to 6 o'clock, we look at it and it looks like it went down several degrees. So we take a look at that and we say 6 o'clock temperature of 70 degrees minus the 5 o'clock temperature of 84 degrees is equal to, and remember how we do this, we add the opposite and we can just subtract the numbers. So there's a difference of 14 and the 84 is larger, which is negative. So it means that we went down 14 degrees and we can see that we did go down, so it should be a negative number. From 6 o'clock to 7 o'clock, the 7 o'clock temperature is 76 minus the 6 o'clock temperature, which is 70. You can add the opposite, or the first number is bigger and it's a positive number anyway, so we should just be able to subtract and find out that that's 6 degrees. From 7 to 8, 8 o'clock is 75 degrees minus 76 degrees that we were the hour before, and again we're going to add the opposite, subtract the two numbers and we have a difference of 1, but 76 is larger, so it's a negative 1 degree. From 8 o'clock to 9 o'clock, we go from 72 degrees at 9 p.m., but it was 75 degrees, so we're going to subtract that from 8 o'clock, and again we're going to add the opposite. The difference between 72 and 75 is 3, but 75 is larger, so it's a negative 3 degrees, and this final one is non-applicable because we don't know what 10 o'clock is. Let's look at this example. Ronda has 152 dollars and 35 cents in her checking account. She deposits, so remember that deposits means she adds money to her account of 423 dollars and 45 cents, and then she writes checks, and when we write checks, we're going to subtract, so it's 135 that she has to take out of her account and 93 dollars and 58 cents, and then also 350. So they ask us to write an expression and apply the sign rule so we can find out how much she has in her account after all of that, so think about it. We start with 152 dollars and 35 cents, and then she deposits 423 dollars, so she adds 423 dollars and 45 cents, and then she's going to subtract 135 dollars, and she's also going to subtract 93.58, and finally she's going to also subtract 350. Those are all her payments. Now before we actually go to the calculator and see this, let's see if we can make sense out of it. She has, it looks like 100 plus 400 would be 500 in approximately 70, 570 dollars, almost 600 dollars, and she's got to pay 135 and 350, 180 plus almost another 100, so she's going to be right on the verge. She may be a little positive, she may be a little negative, we know it will be pretty close, so let's see what it actually is. 152.35 plus 423.45 minus 135 minus 93.58 and minus 350, and her grand total in her account is negative 2.78, so she's in the hole two dollars and 78 cents. Finally, and we have another problem very similar to the one we just did. We see that we have total operating income for 2007, 2008, 2009, and 2010 with these given values. They want us to find the total income, write the expression and use the signs. Well they tell us exactly what the signs are supposed to be, so we have a positive 1037, and then we're going to subtract 4,438, all of these being million, and we're going to subtract a 161 million, and then we're going to add 976. So again before we go to the calculator, let's see if we can make sense out of this. If we have 976 and 1037, that's 1000, this is almost another 1000, so it's about 2000, a little more than 2000, but we already have to subtract 4,000, so this one should be a negative answer. Let's see if it really is. Clear this out. Put in our 1037, minus 4,438, minus 161, and then plus the 976, and we get, sure enough, it's a big number. They are way in the hole because this is $2,586 million in the hole.