SOLUTION: How many quarts of pure antifreeze must be added to 7 quarts of 10% antifreeze solution to obtain a 20% antifreeze solution?

Question 940466: How many quarts of pure antifreeze must be added to 7 quarts of 10% antifreeze solution to obtain a 20% antifreeze solution?
Answer by macston(5194) (Show Source): You can put this solution on YOUR website!
It is best to consider the part of the problem that is not changing, the amount of water. In 7 quarts of a 10% antifreeze (90% water) solution there is
0.90(7 quarts)=6.3 quarts of water. To make a 20% solution (80% water)with 6.3 quarts of water, we need 6.3/.80=7.875 quarts total. So to make 7 quarts of 10% solution 20% we must add 0.875 quarts of pure antifreeze to make a total of 7.875 quarts.
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