How many gallons of a 5% salt solution must be mixed with 20 gallons of a 7% solution to obtain a 6% solution

Answer 1

20 gallons

6 is halfway between 7 and 5, so equal amounts are needed. 20 gallons of 7% and 20 gallons of 5% will yield 40 gallons of 6%

.07(20) + .05x = .06(20+x) = 1.2 + .06x

.01x = 1.4-1.2= .2

x = .2/.01 = 20 gallons of 5%