A cell culture doubles in volume every hour. If it takes exactly 24 hours to completely fill a petri dish at midnight, at what time was the dish one-quarter full?
10:00 PM
Since the culture doubles every hour, working backward: at 11:00 PM (1 hour before full), it was half full. At 10:00 PM (2 hours before full), it was one-quarter full.
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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