SOLUTION: A mixture of 6% disinfectant solution is to be made from 7% and 4% disinfectant solutions. How much of each solution should be used if 21 gallons of 6% solution are needed?

Algebra ->  Percentage-and-ratio-word-problems -> SOLUTION: A mixture of 6% disinfectant solution is to be made from 7% and 4% disinfectant solutions. How much of each solution should be used if 21 gallons of 6% solution are needed?       Log On


   

Question 906799: A mixture of 6% disinfectant solution is to be made from 7% and 4% disinfectant solutions. How much of each solution should be used if 21 gallons of 6% solution are needed?
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
a+b=21,
0.07*a+0.04*b=0.06*21
a=21-b
0.07*(21-b)+0.04*b=1.26
1.47-0.07b+0.04*b=1.26
-0.03*b=-0.21
b=7
a=21-b
a=14 gal at 7%
b=7 gal at 4%
check
0.07*14+0.04*7=0.06*21
0.98+0.28=1.26
1.26=1.26
ok