Calculate how much 30% alcohol solution and 80% alcohol solution must be mixed to end up with exactly 14 gallons of a 40% alcohol solution. You'll need ____ gallons of the 80% solution.

Well it tells you how much 80% solution u need. It's ____. As for the 30%, just guess. That's the best way! (-:

Let the number of gallons of 30% solution =G

Then, the number of gallons of 80% solution =14 - G

[0.3G + 0.8(14 - G) ] =0.4 x 14, solve for G

G =56/5 =11.2 gallons of 30% solution

14 - 11.2 =2.8 gallons of 80% soltution.