Two cans of milk contain 25% water and 50% water respectively. How much milk must be taken from the two cans to get 12 litres of milk so that it will contain water and milk in the ratio 3 : 5?

Can A contain 25% water, so it has 75% milk.

Can B contain 50% water, so it has 50% milk.

We want milk  of 12 litters, with a water-to-milk ratio of 3 : 5.

Solution:
Let a liter taken from  Can A and b liter taken  Can B.

So, a + b =12

Milk in Can A = .75a and water = .25a

Milk in Can B = .5b and water = .5b

According to the question

2.25a + 1.5b = 1.25a +2.5b

a = b

Therefore, 2a = 2b = 12

Or, a = b = 6.

Thus, 6 liters milk should be taken from Can A and Can B.