SOLUTION: A chemistry instructor has one solution that is 50% sulfuric acid and another that is 20% sulfuric acid. How much of each should she use to make 12 liters of a solution that is 30%

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Question 179667: A chemistry instructor has one solution that is 50% sulfuric acid and another that is 20% sulfuric acid. How much of each should she use to make 12 liters of a solution that is 30% acid?
Answer by Mathtut(3670) About Me  (Show Source):
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A chemistry instructor has one solution that is 50% sulfuric acid and another
that is 20% sulfuric acid. How much of each should she use to make 12 liters of a solution that is 30% acid?
:
let x and y be the amount of 50% and 20% solutions respectively
:
x+y=12.......eq 1
.5x+.2y=.3(12)....eq 2
:
rewrite eq 1 to x=12-y and plug it into eq 2
:
.5(12-y)+.2y=3.6
:
6-.5y+.2y=3.6
:
-.3y=-2.4
:
highlight%28y=8%29amount of 20% solution
:
highlight%28x=12-8=4%29amount of 50% solution