Anna is currently twice as old as Ben was when Anna was as old as Ben is now. When Ben is Anna's age now, the sum of their ages will be 63. How old is Anna today?
28
Let Anna's current age be A and Ben's be B. The age difference is A - B. In the past, Ben's age was B - (A - B) = 2B - A, and Anna's age was B. We are given A = 2(2B - A) which simplifies to 3A = 4B. In the future when Ben is A, Anna's age is A + (A - B) = 2A - B. The sum of their ages then is A + (2A - B) = 63, meaning 3A - B = 63. Substituting B = (3/4)A gives 3A - 3A/4 = 63, so 9A/4 = 63, yielding A = 28.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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