In a 60 liter solution of acid and water, the ratio of acid and water is 3 : 7. How much (in liter) acid is to be mixed in the solution so that the ratio of acid and water in the resulting solution is 1 : 2?

3

Acid : Water.

 3    :   7

⇒ (3 + 7)units = 60 L

⇒ 10 units = 60L

⇒ 1 unit = 6 L

⇒ Acid = 3 x 6 = 18 L

⇒ Water = 7 x 6 = 42 L

⇒ Amount of acid to be added to make ratio 1 : 2

⇒ 2 units = 42,

⇒ 1 unit = 21,

⇒ 21 - 18 = 3 L

⇒ Therefore 3 L acid to be added to make ratio of acid and water 1 : 2.