How many litres of milk with 24% concentration are to be mixed with 18 litres with 72% concentration to get a mixture with 36% concentration?

Correct option is B

Given:

Milk A: 24% concentration

Milk B: 72% concentration

Quantity of Milk B = 18 litres

Resultant concentration = 36%

Solution:

Let quantity of Milk A = x litres

Ratio = $$\frac{72 - 36}{36 - 24} = \frac{36}{12} = 3 : 1$$​​

This means Milk A : Milk B = 3 : 1

​$$\frac{x}{18} = \frac{3}{1}$$​​

​$$x = 3 \times 18 = 54$$​​

54 litres of milk with 24% concentration should be mixed

Alternate Solution: ​

Quantity of milk B = 18 litre 

​$$\frac{A}{18} = \frac 31 \\ \ \\ \implies A = 54 \ litre$$​​