20 litres of a mixture contains milk and water 4 : 1. Then the amount of water to be added to the mixture so as to have milk and water in ratio 2 : 1 is-

Question: 20 litres of a mixture contains milk and water 4 : 1. Then the amount of water to be added to the mixture so as to have milk and water in ratio 2 : 1 is-

Solution:
In 20 litres of mixture,
quantity of mik = 20 × (4/5) = 16 litres
quantity of water = 20 × (1/5) = 4 litres
Let,
The quantity of water be added m litres
ATQ,
16 : (4 + m) = 2 : 1
or, 16/(4 + m) = 2/1
or, 2m + 8 = 16
or, 2m = 16 - 8
or, 2m = 8
∴ m = 8/2 = 4

∴ 4 litres water to be added to the mixture.