Answer:
Step-by-step explanation:
10 gallons of the 20% solution contain 2 gallons of bleach.
x gallons of the 5% solution contain 0.05x gallons of bleach.
If the two are combined, the resulting 10+x gallons contain 2+0.5x gallons of bleach. The concentration is (2+0.05x)/(10+x).
(2+0.05x)/(10+x) = 15%
2+0.05x = 0.15(10+x)
2+0.05x = 1.5+0.15x
0.5 = 0.10x
x = 5
5 gallons of 5% solution is added to the 10 gallons of 20% solution.
