How many gallons of 5% acid solution should be mixed with 20 galllons of a 10% acid solution to obtain an 8% acid solution

Answer 1

let the amount of the 5% solution that must be added be x gallons
.05x + .10(20) = .08(20+x)
times 100
5x + 10(20) = 8(20+x)
5x + 200 = 160 + 8x
-3x = -40
x = 40/3

they should add 13 1/3 gallons of the 5% solution.