00:01
So this year ross buys x books for price p each.
00:11
So he spends x times p which is equal to the twelve hundred dollars that he spends every year.
00:22
And then it's projected that the price of the book will go up to p plus five.
00:28
And he can buy 20 books less.
00:32
So he'll buy x minus 20 and still spend the twelve hundred dollars.
00:40
So now we have x p plus five x minus 20 p minus 100 is equal to twelve hundred.
00:58
We also know that x p is equal to twelve hundred.
01:03
So that means that five x minus 20 p minus 100 is zero.
01:12
Or five x minus 20 p is equal to zero.
01:21
And x p is still equal to twelve hundred.
01:26
So that means that x is equal to twelve hundred divided by p.
01:33
So we have five times twelve hundred over p minus 20 p.
01:44
This should be a hundred is equal to 100.
01:48
Multiply everything by p...