Question

A book seller a book for Rs 70 at a gain of 40 percent find the profit

Answer 1

let cost price = x
selling price = x+40% of x
                70= x + (40/100)*x
               70  = x +(40x/100)
                  70  = (100x + 40x)/100
                  70= 140x/100
                   x= (70*100)/140
                   x= 50

Profit = selling price- cost price
profit = 70 -50 =20

Answer 2

solution
s.p= 70
gain=40%

s.p=(100+gain%) /100× c.p
=70=100 + 40% / 100× X
X= (70 × 100) / 140
X = Rs.50
c.p is Rs. 50
profit = 70- 50= 20