SOLUTION: A tank contains 20 gallons of antifreeze solution. When it is full, it contains 15% antifreeze. How many gallons must be replaced by an 80% antifreeze solution to get 20 gallons

Question 529835: A tank contains 20 gallons of antifreeze solution. When it is full, it contains 15% antifreeze. How many gallons must be replaced by an 80% antifreeze solution to get 20 gallons of a 70% solution?
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
Let = gallons of 15% antifreeze to be
removed and replaced with 80% antifreeze
In words:
( gallons of pure antifreeze at end)/( gallons of solution at end) = 70%
-------------
gallons of pure antifreeze at start
gallons of solution left after removal of gallons
= pure antifreeze left after removal of gallons
= pure antifreeze in 80% solution added
The total gallons of solution has not changed

16.923 gallons must be removed and replace with
16.923 gallons of 80% antifreeze
-----------
check:
gallons of solution left after removal of gallons
= pure antifreeze left after removal of gallons
= pure antifreeze in 80% solution added

error due to rounding off- OK

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