Question 631657
A cylinder contains 50 liters of a 60% chemical solution.  How much of this solution should be drained off and replaced with a 40% solution to obtain a final strength of 46%?
.
Let x = amount (liters) of 40% solution 
then
.60(50-x) + .40x = .46(50)
30-.60x + .40x = 23
30-.20x = 23
-.20x = -7
x = -7/(-.20)
x = 35 liters