Question

A shopkeeper buys a number of books for Rs. 80. If he had bought 4 book for the same amount, each book would have cost him Rs 1 less. How manny books did he buy?

Answer 1

He bought 16 books in the beginning.
Hope this helps you.

Answer 2

ANSWER :

Let the number of books brought be x.

Then, the price of x books be = Rs 80

Cost of one book be = Rs 80/x

If the no. of books bought is x + 4 then,

Price of one book = Rs 80 /x + 4

According to the given Question price of 1 book is reduced by 1 rupee.

Therefore, 80/x - 80/x+4 = 1

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

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

320/x²+ 4x = 1

x² + 4x = 320

x² + 4x - 320 = 0             ( middle term splitting )

x² + 20x - 16x -320 = 0

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

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

x = ₋ 20 or , x = 16

$\implies \boxed{\mathsf{x = 16 }}}$

( we don't choose x = - 20 Because x cannot be in negative..always in positive )