Self doubt in percentage and mixtures

Question

In a mixture of 80 litres of milk and water, 25% of the mixture is milk. How much water should be added to the mixture so that milk becomes 20% of the mixture?
(a) 20 litres
(b) 15 litres
(c) 25 litres
(d) None of these

Answer 1

(a) $20$ litres.

Amount of milk= $25$% of $80 $=$20$ litres.

If we add 20 litres of water. %age of milk=$\frac{20}{100}$=$20$%