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?

5 flies have made the attempt. Since survival/non-survival is equally likely, either
a)Survivors are in the 'majority' (3 or more) and the spider is still hungry
or
b)The non-survivors are in the majority - the spider is full and a safe passage for the 6th fly is assured.
So half the time the 6th fly is safe and half the time he has a 50% survival rate
p=.5 + .5*.5
p=.75 (or 75%)

Posted by Lee on 2003-11-26 13:53:19