Question

In 80 litres mixture of milk and water the ratio of amount of milk to that of amount of water is 7 : 3. in order to make this ratio 2 : 1, how many litres of water should be added?

Answer 1

Given that volume of mixture = 80 litres
Milk. Water
56 litres. 24 litres .....(1)
56 litres. 24+ X litres.....(2)

the ratio of milk and water is 7:3 then the volume of milk and water written above.
now let we mix X litre of water in mixture then ratio of volumes of milk and water is 2:1
now

$\frac{56}{48 + x} = \frac{2}{1} \\ 56 = 48 + 2x \\ 2x = 8 \\ x = 4$
So we need to mix 4 litres of water.