Question

A shopkeeper buys some books to Rs.80. If he had bought 4 more books for the same amount each book would have cost Re.1 less. Find the number of books he bought

Answer 1

Let the shopkeeper buy x number of books.

According to the given condition, cost of x books = Rs. 80

Therefore cost of each book = Rs. 80/x

Again, when he had bought 4 more books, then total number of books in this case = x + 4

So, cost of each book in this case = Rs. 80/x+4

According to the question,

Cost of each book in first case - cost of each book in second case = 1 Rupee

80/x - 80/x+4 = 1

80(x+4) - 80x / x(x+4) = 1

x^2 + 20x - 16x - 320 = 0

(x - 16)(x + 20) = 0

x = 16 or x = -20

Hence, the shopkeeper bought 16 books.