Elvin is trying to make chocolate milk that is 15% chocolate syrup. How many gallons of chocolate milk that is 20% chocolate syrup does he need to mix with half a gallon of chocolate milk that is 12% chocolate syrup to make his desired drink?
Let G be the 20% mixture we need
We have this equation
.20G + (.12) (1/2) = (.15) (G + 1/2) simplify
.2G + .06 = .15G + .075 subtract .15G, .06 from both sides
.05G = .015 divide both sides bu .05
G = 015 / 05 = ,3 gal of the 20% mixture