Math CentralQuandaries & Queries


Question from John, a student:

Lisa is 15 years old. Marcus is 49 years old. How old will they both be when Marcus is three times as old as Lisa?

Hi John.

You can use algebra to solve this puzzle.

Let Y = some number of years from now.

At that point in time, Lisa will be (15 + Y) years old and Marcus will by (49 + Y) years old.

That's when Marcus is three times as old as Lisa, so we know that

3 (15 + Y) = (49 + Y)

Does this help? Can you solve the problem now?
Stephen La Rocque.

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