Need help with a math problem

Question

How many gallons of 8% solution must be mixed with 12 gallons of 4% solution to rproduce 5% solution? I ended up getting -15.2 gallons any way I work it and I just want to make sure that's correct.

Answer 1

Alex, your answer can't be negative!

 

Let s = the # of gallons of 8% solution.

 

.08s + .04(12) = .05(s + 12)

.08s + .48 = .05s + .6

.03s = .12

s = 4

 

4 gallons is your answer.