Question 590967
You want to know what volume, 'v,' is left from the initial draining. We must have (0.6*v)/(v+w)=0.5 for the volume 'w' of water added. We also know that v+w=12. Thus, (0.6/12)*v=0.5 and v=10, so we must drain 12-10=2 quarts of solution and then replace it with water.