Logic Puzzles

7. The Frog

A frog is at the bottom of a 30 meter well. Each day he summons enough energy for one 3 meter leap up the well. Exhausted, he then hangs there for the rest of the day. At night, while he is asleep, he slips 2 meters backwards. How many days does it take him to escape from the well?

Note: Assume after the first leap that his hind legs are exactly three meters up the well. His hind legs must clear the well for him to escape.

Submitted by GmdAquaman · Added 1 January 2007

Hint:

Try to think the problem through for a five meter well. Now what is the solution for the 30 meter well?

Solution:

28

Each day he makes it up another meter, and then on the twenty eighth day he can leap three meters and climb out.


Comments (15)

Anonymous 22 March 2010

7 doesn't make sense. can you explain it thoroughly

Anonymous 20 April 2010

It should be 28 days as on the morning of the 27th, the frog has only jumped 26 meters.

Anonymous 14 July 2010

The answer seems to be wrong. It says the answer is 28 but the explanation says 27.

Anonymous 18 March 2011

Dear sir/ Madam, I love the site, but I have a question. On the problem 7. The Frog, why is the answer 28 and not 27? Thank you in advance. Lislene

Anonymous 18 March 2011

On the problem 7. The Frog, why is the answer 28 and not 27?

Anonymous 14 August 2011

He exits exactly 27 days after making his first jump, on his 28th jump. The explanation gives the correct answer, but the numeric answer is wrong.

Anonymous 14 August 2011

The Frog puzzle has a numerical error in the answer. He exits exactly 27 days after making his first jump, on his 28th jump.

Anonymous 18 October 2011

The burglar would take longer to escape the building due to the presence of banks.

Anonymous 8 February 2012

The answer I put was 28 days, but it was marked incorrect. I checked the answer and I was right. Please do fix.

Anonymous 1 May 2012

The fisherman would indeed travel downstream with the flow, which contradicts the initial premise. However, the answer remains two hours.

Anonymous 6 May 2012

number 7 is incorrect. you broke the parameters that you set. the frog needs to rest for a day after a leap. it will take 28 days for his hind legs to clear the ledge. but if climbing is now an option, it will take one day. the frog will simply climb out

Anonymous 6 May 2012

The frog needs to rest for a day after a leap. It will take 28 days for his hind legs to clear the ledge.

Anonymous 7 July 2014

In puzzle 7, the frog, there are two different solutions provided. The correct answer should be 27, not 28.

Anonymous 28 October 2017

The frog problem. Assuming day 1 is the first day he takes a jump, it will be day 28 that he escapes from the well. However, the total amount of time elapsed is 27 days since he made his first jump assuming he jumps at time 0. At t=24 hours he jumps to 4 meters. At t=48 hours he hits 5 meters, etc. At t=648 hours or 27 days, the frog reaches the 30 meter mark. This is why I do not like the solution of it takes the frog 28 days. It only takes the frog 27 completed days since he started.

Anonymous 28 October 2017

Assuming day 1 is the first day he takes a jump, it will be day 28 that he escapes from the well. However, the total amount of time elapsed is 27 days since he made his first jump.

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