Linear Equation Word Problem

Question

How many gallons of a 5% acid solution must be mixed with 5 gal of a 10% solution to obtain a 7% solution?

Answer 1

.05X + .1(5) = .07(X + 5)   The amount of pure acid, concentration * volume, must be equal on both sides.

.05X + .5 = .07X + .35

-.02X = -.15

X = 7.5 gal