capegemini - how many litres of milk worth rs12 per litre must be mixed with 60 litres of milk worth rs8 per litre so as to gain 20 by selling the mixture at rs1080 per litre - skillgun

S.P of 1 litre of mixture = Rs.10.80 and Gain 20%.
Therefore, C.P of 1 litre of mixture = Rs.100/120 x 10.80 = Rs.9 ...(1)
C.P of 1 litre milk of 1st kind = d = Rs.12
C.p of 1 litre milk of 2nd kind = c = Rs.8
Mean Price = m = Rs.9 (from equation 1)
Then d - m = 3 , m - c = 1
Applying above values to our allegations formula (refer introduction before question)
Ratio of quantities of 1st and 2nd kind = 1:3 .Assume x litres of milk of 1st be mixed with 60litres of 2nd kind.
Then, 1 : 3 = x : 60
1/3 = x/60
x = 60/3 = 20.
Thus 20 litres milk of 1st kind to be mixed with 2nd.