A water lily doubles in size every single day. If it takes 30 days for the lily to completely cover an entire pond, how many days did it take for the lily to cover exactly half of the same pond?
29 days.
Since the lily doubles every day, whatever state it is in on day N, it was half that size on day N-1. Therefore, it covered half the pond on day 29.
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: Easy. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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