Bunuel wrote:
A sample of x litres from a container having a 60 litre mixture of milk and water containing milk and water in the ratio of 2 : 3 is replaced with pure milk so that the container will have milk and water in equal proportions. What is the value of x?
A. 6 litres
B. 10 litres
C. 15 litres
D. 20 litres
E. 30 litres
Conc of milk in mixture (C1) = 2/5
Conc of milk in pure milk (C2) = 1
Conc of milk in new mix (Cavg) = 1/2
w1/w2 = (1 - 1/2) / (1/2 - 2/5) = (1/2) / (1/10) = 5/1
So original mixture was 5 parts and pure milk was 1 part to get equal proportions of milk and water. Total 6 parts is actually 60 litres which means the 5 parts are 50 litres and 1 part is 10 litres.
Hence 10 litres of original mix was replaced with pure milk.
Answer (B)
Check this post:
https://www.veritasprep.com/blog/2012/0 ... -mixtures/Answer (B).