Problem:
Jar  contains four liters of a solution that is  acid. Jar  contains five liters of a solution that is  acid. Jar  contains one liter of a solution that is  acid. From jar  liters of the solution is added to jar , and the remainder of the solution in jar  is added to jar . At the end both jar  and jar  contain solutions that are 50% acid. Given that  and  are relatively prime positive integers, find .
Solution:
If the contents of all three jars were mixed together, the mixture would be ten liters that is acid. Thus the total amount of acid in the three solutions is , so . When liters from jar are added to jar , the final proportion of acid in jar is . Solving gives , and so the requested sum is .
The problems on this page are the property of the MAA's American Mathematics Competitions