A spider eats 3 flies a day. Until the spider fills his quota a fly has a 50% chance of survival if he attempts to pass the web.

Assuming 5 flies have already made the attempt to pass, what is the probability that the 6th fly will survive the attempt?

Well, I was wrong in my first solution in the assumption, that all 26 allowed possibilities after first 5 attempts have the same probability - they dont. 10 possibilities, where 3 flies are eaten have a probability of 50% of happening and rest 16 possibilities have probability of 50% as well.

So correct solution is: 0,5*1+0,5*0.5=75%. Sorry for confusion.

Posted by Saso on 2003-11-25 09:45:18