Question

a person sells a book for rs 11.he gains as many percent as its cost price in rupees. what is the cost price?

Answer 1

$cp = \frac{100}{100 + gain \: percent} \times sp \\ cp = \frac{100}{111} \times 11 = 9.09$
so cp=9.09

Answer 2

A book price is of Rs 11 you have to find the cost price.

The formula is of Gain%=SP-CP/CPX100.

But to find CP, CP=100/100+gain percent *SP, => CP=100/111* 11, =>CP= 9.09.

Therefore the cost price of the book is of 9.09 if in case you get negative value omits it.