Interview Question: Frog in the Well

Sample Question #140 (brainteaser)

The allegorical frog in the well is finally determined to see the world outside for himself and begins to climb out of the well it’s been living in all its life. The well measures 10 feet deep. The frog climbs three feet a day, but when it sleeps at night, it slides down the wall by one foot. How many days does it take the frog to reach the top?

[A childhood puzzle from my elementary days in China]

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2 Responses to Interview Question: Frog in the Well

  1. Brett says:

    ANSWER
     
    Obviously, after one day and one night, the frog has gone up 2 feet. By the third morning, it has gone up a total of 4 feet. By the fifth morning, it has climbed a total of 8 feet. So sometime in the fifth day, it climbs out of the well. As an interviewer I would accept the answer "5 days," but I’m sure some interviewers would insist on the "textbook-correct" answer of 4 2/3 days, since the frog does not need to climb 3 feet on the fifth day.
     

  2. Wu Chao says:

    hehe, we share the same question in childhood. If the interview insists on the 4 2/3, he sucks. haha..

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