Question

A shopkeeper buys a number of books for Rs 840. If he had bought 5 more
books for the same amount, each book would have cost Rs 4 less. How
many books did he buy?​

Answer 1

Step-by-step explanation:

Let the shopkeeper buy x number of books.

According to the given condition cost of x books =Rs840

Therefore cost of each book =

x/840

Again when he had brought 5 more books

Then total books in this case =x+5

So cost of each book in this case =

x+5/840

According to Question,

840/x-840/(x+5) =4

840(x+5) -840x/x(x+5) =4

4xsq+20x-4200=0

2xsq+10x-2100=0

(2x+70) (x-30) =0

x=30 or x=−35

Hence the shopkeeper brought 30 books