Service Station

Question

A service station checks Mr. G's Radiator and finds it with 30% antifreeze. If the radiator holds 10 quarts how much must be drained and replaced with pure antifreeze so it creates 50%

Answer 1

Let x be amount of pure antifreeze (100%) you need to replace and there you would have 10-x left (30%) in the radiator after it's drained. It is still 10 quarts (50%) at the end. 

x*100%+(10-x)*30%=10*50%

x+3-0.3x=5

0.7x=2

x=2.86 quarts approximately