The price of pure mustard oil is Rs 100 per litre.A shopkeeper adulterates it with some other types of oil at Rs 50 per litre. He sells the mixture at the rate of Rs 96 per litre so that to gain 20% on whole transaction. The ratio in which he mixed the two oils is:
(A) 1 : 2                     (B) 2 : 3                    (C) 3 : 2                      (D) 1 : 4                 (E) None of these

Let pure oil = x litres and

other oil = y litres 

Profit=20% 

Cost of pure oil is Rs. 100x and 

Cost of other oil is Rs. 50y.

Total Cost price (CP) = Rs. (100x + 50y)

Now, the shopkeeper sell mixture =   (x+y) litres of adulterated oil at the rate of 96 Rs/litres.

Total Sale Price (SP) = 96(x+y) = 96 x + 96y

Profit = SP-CP = [96x+96y] - [100x+50y] = 46y-4x

The shopkeeper  has to mix pure and other oil in the ratio 3:2