A mixture of 6% disinfectant solution is to be made from 7% and 3% disinfectant solutions. How much of each solution should be used if 20 gallons of 6% solution are needed?

Answer 1

5 gallons of 3% plus 15 gallons of 7% will yield 20 gallons of 6%

7 is within 1 of 6

3 is within 3 of 6

you need 3 times as much of 7% as of 3%. 15 = 3 x 5

7x + 3(20-x) = 6(20) = 120

7x -3x = 120 -60 = 60

4x = 60

x = 60/4 = 15 gallons of 7%

20-x = 5 gallons of 3%

7(15) + 3(5) = 105 + 15 = 120