Question

A shopkeeper buys a no. Of books for RS 80.if he had bought 4 more books at the same cost.each book would cost 1rs less.how many books did he purchase

Answer 1

Lets suppose he bought X books,
so, X books cost = Rs.80
1 book cost = RS
If he had bought 4 more books then,
(X+4) books cost = Rs. 80
(since it is given that he had bought 4 more books at the same cost as when he bought X number of books)
1 book cost = Rs.
Therefore,
According to the question,
(price per book when he bought X number of books-price per book when he bought X+4 number of books=1)
that is,
()=1
=> 80(X+4-X)=+ 4X
=> + 4X - 320 =0
=> X(X+20) - 16(X+20)=0
=> (X+20)(X-16)=0
So, X can have two values : (16,-20)
-20 is ignored as number of books cannot be negative.
Thus the answer is 16.
Hope you understand