How much pure alcohol should be added?

Question

A 10-gallon alcohol-water solution contains 30% pure alcohol. How much pure alcohol should be added to produce the solution to 34% alcohol ?

Answer 1

10(.3) + x = (10+x)(.34) solve for x

3 +x = 3.4 +.34x

.66x = .4

x = .4/.66 = 40/66 = 20/33 of a gallon

=- about 0.606 gallon