The ratio of milk and water in a 30 litre mixture is 3 : 2. Find the quantity of water to beadded to the mixture in order to make this ratio 1:1.

Correct option is D

Given:

The total volume of the mixture = 30 litres

The ratio of milk to water in the mixture = 3 : 2

We need to find the quantity of water to be added to make the ratio of milk to water 1 : 1

Solution: 

Let the quantity of water to be added be x

Current quantity of milk in the mixture:

$$= \frac{3}{5} \times 30 = 18 \, \text{litres}$$​​

Current quantity of water in the mixture:

$$= \frac{2}{5} \times 30 = 12 \, \text{litres}$$​​

After adding x litres of water, the new quantity of water will be:

= 12 + x

The new ratio of milk to water should be 1:1, so:

$$\frac{18}{12 + x}$$​ = 1

18 = 12 + x

x = 18 - 12 = 6litres

Therefore, the quantity of water to be added is 6 litres

Alternate Solution: 

old Ratio(milk : water) =  3  :  2

new ration (milk : water) = 1 : 1 

water is added, so the milk ratio remains same 

so, new ratio became (milk : water) = 3 : 3 

Now, difference in water ratio  (new to old ) = 3 - 2 = 1 

5 unit = 30 litre 

1 unit = 6 litre 

Thus, 6 litre of water added