A grandfather, his son, and his grandson share the same birthday. The grandfather's age in years is equal to the grandson's age in months. The sum of all three of their ages is 120 years. How old is the father?
55 years old
Let the grandson's age in years be G. His age in months is 12G, making the grandfather 12G years old. With Father's age as F, the sum is 12G + F + G = 120, or 13G + F = 120. If G = 5, the grandfather is 60 and the grandson is 5. Substituting these gives 13(5) + F = 120, so F = 55. This makes logical sense as 60 > 55 > 5.
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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