Five gallons of a 45% acid solution is obtained by mixing a 90% solution with a 30% solution. How many gallons of each solution must be used to obtain the desired mixture?

Answer 1

Let x = number of gallons of 90% solution

Then, 5 - x = number of gallons of 30% solution

0.90x + 0.30(5 - x) = 0.45(5)

0.90x + 1.5 - 0.30x = 2.25

0.60x = 0.75

x = 1.25 gal

Use 1.25 gal of 90% solution and 3.75 gal of 30% solution.

Answer 2

(90x+30y)/(x+y)=45x+45y

x+y=5gal

-90 -30

=45 15

5/60=.083