Question 179663
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(y=8)}}}amount of 20% solution
:
{{{highlight(x=12-8=4)}}}amount of 50% solution