BrainDen.com - Brain Teasers
• 0

## Question

did anyone post this before. maybe this is quite easy.

A frog is trap under 20 meter holes. Once it jumps, it can jump 5m but slide 4m downwards. How many times it(the frog) must jumps??

## 9 answers to this question

• 0

15 times would get the frog out.

Each jump jump before the 15th will progress it a meter toward the top, since each jump gives 5m, but then slides back 4m as it rests. So that after the 14th jump, it jumps from the 14m mark to the 19m mark but slides back to the 15m mark. But the next jump would get it out. Since at the 15m mark, it can jump right to the 20m mark, where the exit of the hole is.

##### Share on other sites
• 0

11

did anyone post this before. maybe this is quite easy.

A frog is trap under 20 meter holes. Once it jumps, it can jump 5m but slide 4m downwards. How many times it(the frog) must jumps??

##### Share on other sites
• 0

16 because if the hole itself is 20, when the frog jumps the 15th time, it will reach exactly the brim, but not out, so it would slide 4 down, and then jump one more and be out of the hole.

##### Share on other sites
• 0

15 times would get the frog out.

Each jump jump before the 15th will progress it a meter toward the top, since each jump gives 5m, but then slides back 4m as it rests. So that after the 14th jump, it jumps from the 14m mark to the 19m mark but slides back to the 15m mark. But the next jump would get it out. Since at the 15m mark, it can jump right to the 20m mark, where the exit of the hole is.

close but

16 jumps. 15 jumps get him to 15 feet and the 16th jumps him out.

• 0

20 times

##### Share on other sites
• 0

16 would take it right to the lip of 20, or 17 if you'd like it to jump out above the very edge.

On the first jump, he goes up to 5 and ends up at 1. Second jump, he goes up to 6 and ends up at 2. You can see that after 15 jumps, he hits 19, but lands at 15. On the 16th jump he hits 20 feet.

##### Share on other sites
• 0

Who says the hole is 20m deep, could be 20m in diameter and less than 5 m deep and he can get out in 1 jump.

##### Share on other sites
• 0

This is a variation of an old problem - one which I have been using on my maths classes for at least 20 years!

Th version I know is this:

A man is trapped 20 m down in a well. Every hour, he climbs up 3 m, but then falls back 2 m. How many hours will it take him to get out of the well?

The idea is exactly the same as this posted problem. There are a number of similar problems which are well-known.

The answer is of course 18 hors. In the last hour, he doesn't fall back 2 m, because he's out.

##### Share on other sites
• 0

Who says the hole is 20m deep, could be 20m in diameter and less than 5 m deep and he can get out in 1 jump.

Good out of the "hole" thinking!

Welcome nikss to the den. Dont get surprised by such out of the box answers, you'll find plenty of it here! If I may quote Bonanova which went something like this - some people here are living so far out of the box that if you ask them to think within the box, they need to first find the box

## Create an account

Register a new account