Question

A shopkeeper buys a number of books for Rs80. If he had bought 4 more books for the same amount, each book would have cost Rs1 less. How many books did he buy?​

Answer 1

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Let the shopkeeper buy x number of books.

According to the given condition cost of x books =Rs80

Therefore cost of each book = 80/x

Again when he had brought 4 more books

Then total books in this case = x + 4

So cost of each book in this case = 80/(x + 4)

According to Question,

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 brought 16 books.