A container holds bacteria that double in population every minute. At minute 10, the container is half full. At what minute was the container one-quarter full?
Minute 9
Since the population doubles every minute, working backward means the population was half its current size one minute prior. Half of half is one-quarter, so it was one-quarter full at minute 9.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Easy. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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