A family of four—Dad, Mom, Son, and Daughter—are ages 40, 38, 12, and 10 respectively. In how many years will the sum of the children's ages equal half the sum of the parents' ages?
4 years
Current parents' sum = 40 + 38 = 78. Current children's sum = 12 + 10 = 22. In y years, parents' sum increases by 2y (y for each parent), and children's sum also increases by 2y (y for each child). We want children's sum + 2y = 0.5 * (parents' sum + 2y). 22 + 2y = 0.5 * (78 + 2y). 22 + 2y = 39 + y. y = 17? Wait. 2y - y = 39 - 22 = 17. Let's check: In 17 years, parents are 57 and 55 (sum 112). Children are 29 and 27 (sum 56). Half of 112 is 56. Perfect!
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: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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