How many gallons of a 5% salt solution must be mixed with 60 gallons of a 7% solution to obtain a 6% solution?

Question

 How many gallons of a 5% salt solution must be mixed with 60 gallons of a 7% solution to obtain a 6% solution?

 

Answer 1

(x gal)(5%) + (60 gal)(7%) = (60 + x gal)(6%)

5x + 420 = 360 + 6x

-x = -60

x = 60

So you need 60 gal of 5% to be mixed with 60 gal of 7% to obtain120 gal of a 6% solution.