A container holds a colony of bacteria that doubles in size every minute. If it takes 60 minutes for the container to become completely full, at how many minutes was the container exactly half full?
59 minutes
Since the population doubles every minute, working backward one minute from full (60 minutes) means it was half full at 59 minutes.
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: Hard. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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