Question

how much of a 10% alcohol solution must be mixed with 20 gallons of a 15% alcohol solution to obtain a solution that is exactly 13% alcohol

Answer 1

13 1/3 gallons of the 10% alcohol solution should be mixed

Let the number of gallons of alcohol be x

10% of x + 15% of 20 = 13% of (x+20)

0.1(x) + 0.15(20) = 0.13(x + 20)

0.1x + 3 = 0.13x + 2.6

3-2.6 = 0.13x-0.1x

0.4 = 0.03x

x = 40/3

x = 13 1/3 gallons