[Guest]

You enter the following tunnel system at the starting point (marked "S"). If you exit through the tunnel marked "W", you win a fabulous prize. If you exit through a tunnel marked "L", you lose and get nothing.

At each intersection, you must make a choice which to go. You may only go East, West, or South; never North. You may not backtrack. So, at each intersection you flip a coin to decide which direction to proceed.

What is the probability that you will win the fabulous prize?

Note: There is ONE path where using the above rules can get you stuck, i.e. you cannot make a valid move. For this path ONLY, assume backtracking is ok.

[Guest]

9.375, i differ with you voltage only on the spots where you dont make a choice cause you know it will eventually led north (you should still have to flip the coin on those spots, imo)

meaning you can get caught in a dead end.

good riddle, i thought north thing could have been incorporated as long as you dont allow ppl to repeat part of their path, what i would categorize under backtracking, that way you avoid those loops

[Guest]

Ok I made a bit of a mistake here:

neida and DanCDow got the right answer quite awhile ago, but neither gave a satisfactory justification.

voltage, you are correct, and your logic is good.

raschaller, if you cannot go North, then you would never flip the coin to choose between North and another direction. It is not an automatic L, it is simply a way to constrain your movement through the maze.

My apologies for the confusion over backtracking and heading north. I need to try to think these things out a little better to avoid confusion

I agree, and I think this post shows reasonable justification:

http://brainden.com/forum/index.php?s=&amp...st&p=126241

[Guest]

9.375, i differ with you voltage only on the spots where you dont make a choice cause you know it will eventually led north (you should still have to flip the coin on those spots, imo)

meaning you can get caught in a dead end.

As mentioned earlier, if you get caught in a dead end you are allowed to backtrack to the previous intersection. Flipping a coin at an intersection with North makes no difference: If you come to a spot where you can go North or East, regardless of your coin flip you MUST go East, thus the probability of you going East at that intersection is 1.

[Guest]

I agree, and I think this post shows reasonable justification:

http://brainden.com/forum/index.php?s=&amp...st&p=126241

missed your post, sorry. You are right!