 Hello and welcome to the session. In this session we will discuss a question which says that there are 400 fishes in a pond. As per number of fishes die every month due to pollution in the pond. Now in the first part we have to write an expression to show how many fishes were left in the pond after one year and in the second part if it was found that 20 fishes die every month then evaluates the number of fishes left after one year. Now let us start with the solution of the given question. Now the question is given that there are 400 fishes in a pond and it is also given that as number of fishes die every month due to pollution in the pond. Now if number of fishes that die every month is F then number of fishes that die in a year will be equal to 12F. As we know in one year there are 12 months so if number of fishes that die in one month is F then number of fishes that die in 12 months that is in one year will be equal to 12F. Now in the first part we have to write an expression to show how many fishes were left in the pond after one year. Now number of fishes left in the pond after one year will be equal to total number of fishes minus number of fishes that die in one year. Now here total number of fishes are 400 and number of fishes that die in a year are 12F. So putting these values here this is equal to 400 minus 12F. So this is the required expression which shows the number of fishes left in the pond after one year. Now in the second part it is given that 20 fishes die every month then we have to evaluate the number of fishes left after one year. Now here the number of fishes that die every month is denoted by F. So in the second part given F is equal to 20. Now we know that number of fishes left in the pond after one year is equal to 400 minus 12F. Now putting F is equal to 20 in this expression this will be equal to 400 minus 12 into 20 which is equal to 400 minus now 12 into 20 is 240 and this is equal to 160. So 20 fishes die every month then number of fishes left after one year will be 160 and this is the solution of the given question. That's all for this session hope you all have enjoyed this session.