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

Let the num,ber of books be b.

Amount of each bok = `840/"b"`

If the number of books increased to B + 5 , it would have costed `840/"b" - 4`

As the amount is same , hence

`(840/"b" - 4)("b" + 5) = 840`

⇒ (840 - 4b)(b + 5) = 840b

⇒ 840b + 4200 - 4b² - 20b = 840 b

⇒ (b + 35)(b - 30) = 0

Hence , no.of. books = 30