Alcohol solution word problem

Question

Herb has an 80% methyl alcohol solution. He wishes to make a gallon of windshield washer solution by mixing his methyl alcohol solution with water. If 128 ounces or a gallon of windshield fluid should contain 6% methyl alcohol how much of the 80% methyl alcohol solution and how much water must be mixed?

Answer 1

The ratio of the two volumes required is inversely proportional to the ratio  of the concentrations of the Herb's methyl alcohol solution and the windshield fluid

 

This makes sense to us since we know much less than a gallon of Herb's more concentrated solution will be needed to make the gallon of windshield fluid.

 

Therefore the amount needed is 6%/80% gallons = 0.075 gallons.

 

 And therefore 1 - .075 = .925 gallons of water is required.