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PrintSouth African Mathematics Olympiad Second Round
South Africa algebra
Problem
Exactly two years ago the Benson family had 4 members, and their average age was . The Bensons then adopted another child. If the average age of the family today is still , what is the present age of the adopted child?
Solution
2 years ago the sum of all the family's ages was . That should have increased by , but has actually become , i.e. increased by . So the new person is now years old.
Final answer
11
Techniques
Simple Equations