Ants moving on stick brain teaser


Ants on a stick may only face and move toward left or right. When two ants meet each other they bounce off and immediately move in the opposite direction maintaining the same speed entire time. When an ant reaches an end of the stick, it falls off.

If on a 1 meter long stick 25 ants are randomly kept which are moving with a constant speed of 1 meter per minute, what is the longest amount of time it could take for them to all fall off?ants-on-stick-puzzle

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  • 2 Answer(s)
    Yodha Expert Answered on 1st October 2016.
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    We can understand this more easily by breaking down the solution. Let’s say there were 2 ants and both started at the end, and meet in the middle, and then turn in opposite directions and then fall off the stick. So both have completed 1/2 + 1/2 = 1 stick and so takes 1 minute.

    Similarly we can work out this with 3 ants and putting them randomly and check out what happens in each scenario. In all cases time <= 1 minute.So 1 minute (time taken for 1 ant to cross the stick) is the answer.

    radkan Scholar Answered on 29th March 2017.
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