Question 163917
A tank contains 50 gallons of a 40% solution of antifreeze. How much solution needs to be drained out and replaced with pure antifreeze to obtain a 50% solution. 
:
Let x = amt of 40% solution removed, and amt of pure antifreeze added:
:
.4(50 - x) + x = .5(50)
:
Solve this and you should have it.