Question 664662
Establish variable
x = liters of 80%
...
Given
10 l of 30%
x l of 80%
To yield
10+x of 50%
...
Set the equation and solve for x
.3(10) + .8x = .5(10+x)
3 + .8x = 5 + .5x
Group like terms
.8x - .5x = 5 - 3
.3x = 2
Divide both sides by .3
x = 6.7 liters 
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