How much water must be added to a 50% solution of acid to get 20 gallons of a solution that is 10% of acid?

Question

How much water must be added to a 50% solution of acid to get 20 gallons of a solution that is 10% of acid?

Answer 1

You need 4 gallons of your orignal solution (50%) to which you add 16 gallons of water (0% acid) to get 20 gallons of 10% solution.