If a milkman mixes 4ℓ of water in 9ℓ of milk, how much water should he add to 36ℓ of milk to maintain the same ratio of milk and water?

Correct option is D

Given:
Water = 4ℓ, Milk = 9ℓ
Required: Water to be added to 36ℓ of milk to maintain the same ratio

Concept Used:
To maintain the same ratio, the proportion of water to milk must remain constant.

Solution:

Let the water to be added to 36ℓ of milk be x.

​$$\frac{x}{36} = \frac{4}{9}$$

x = $$\frac{4}{9} \times 36 = 16$$

So, 16 ℓ of water should be added.

Thus, the correct answer is (d).

Alternative Method:

Water : Milk

4x : 9x 

9x = 36

x = 4

Water = 4x = 4 $$\times$$​ 4 = 16