How much should he mix from each of the containers so as to get 12 litres such that the ratio of water to milk is 3 : 5?

Question

A milk vendor has 2 cans of milk. The first contains 25% water and the rest milk. The second contains 50% water. How much milk should he mix from each of the containers so as to get 12 litres of milk such that the ratio of water to milk is 3 : 5?

Answer 1

6 litres from each can!
Say the ratio of 12 litre from first container = X, and ratio of 12 litre from second container = Y,
then comparing ratios of milk from each container to final ratio of milk in 12 litre,
=> 3/4X+1/2Y = 5/8
similarly, comparing ratios of water from each container to final ratio of water in 12 litre,
1/4X+1/2Y = 3/8
Solving both equations we get, X=1/2 and Y=1/2...so we will get 12/2 = 6 litres from each container.
check: 3/4*1/2+1/2*1/2 = 3/8+1/4 = 5/8

Answer 2

The first contains 75% milk, and the second contains 50% milk. You want 12 litres of 5/8 milk, or 7.5 litres milk. Let n be the amount of 75% milk, and 12-n be the amount of 50%. Then:
.75n+.5(12-n)=7.5
.25n=1.5
n=1.5/.25=6
12-n=6
The vendor needs 6 litres of each
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