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?

After first 5 attempts, there are 26 allowed possibilities of survival or death of a fly. 16 of them include 3 deaths (quota filled). For these 16 possibilities, next attempt will be successful. For rest 10 possibilities, next attempt will be successful with 50% rate.

So the probability of survival for 6th fly is: P= (10.1+16*0.5)/26=9/13=cca 69,23%

Posted by Saso on 2003-11-25 09:18:32