An 80 litre mixture of water and acid contains 20% acid. How much acid should be added to make the acid 60% in the new mixture?

Let the quantity of new mixture is ‘a’ litres

Acid in the mixture = 20% of 80 litre = 16 litres

Water in the mixture = 80 – 16 = 64 litres = 80% of the mixture

In new mixture water is only 40% and acid is 60%

Water in new mixture = 40% of a litres = 64 litres

⇒ 2/5 × a = 64 litres

⇒ a = 160 litres

Acid in new mixture = 160 – 64 = 96 litres = 60% of the new mixture

∴ Acid that should be added = 96 – 16 = 80 litres