20 liters of a mixture contains milk and water in the ratio 3 : 1. Then the amount of milk to be added to the mixture so as to have milk and water in the ratio 4 :1 is

Ratio of milk and water in 20 litres mixture = 3:1

=> Quantity of milk = $$\frac{3}{(3+1)}\times20=15$$ litres

=> Quantity of water = $$20-15=5$$ litres

Let amount of milk added = $$x$$ litres

According to ques,

=> $$\frac{15+x}{5}=\frac{4}{1}$$

=> $$15+x=20$$

=> $$x=20-15=5$$

$$\therefore$$ The amount of milk to be added to the mixture so as to have milk and water in the ratio 4 :1 = 5 litres

=> Ans - (B)