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Five doors (Posted on 2002-06-05) Difficulty: 3 of 5
Locked in a dungeon, you are faced with five doors. One of them leads to freedom. The other four will lead you back to the starting room disoriented and confused, so that you will not remember which of the doors you have already tried and have to start again.

How many attempts do you expect to make on the average (statistically) before making it out?

See The Solution Submitted by levik    
Rating: 3.8000 (5 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution Simpler Solution | Comment 5 of 11 |
Going through a door, there is an 80% change you will be back in the same situation you were in previously (i.e. not escaped).

So, if N is the average number of doors you will go through to escape, then:

N = 1 + 0.8 * N
0.2 * N = 1
N = 5
  Posted by Nick Reed on 2002-06-06 03:50:41
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