Question

How many gallons of a 20% salt solution must be mixed with 4 gallons of a 30% salt solution to make a 25% salt solution?

Answer 1

Since 25% is smack in the middle between 20% and 30%, it will take equal volumes of ech to make a 25% solution.

Since 4 gallons of 30% solution was used, so 4 gallons of 20% solution will be needed.