A baker put 500 raisins into dough, mixed well, and made 100 cookies. You take a random cookie. What is the probability of finding at least 4 raisins in it?
At first I thought the answer is $ \frac{497}{500} $ because then there would be atleast 4 raisins in a random cookie. But my problem is how do I take 100 cookies in to account?
Hint:
(Using the assumptions I gave in the comments above)
What is the probability of flipping exactly zero heads when flipping five hundred unfair coins where the probability of heads for each was $\frac{1}{100}$?
What is the probability of flipping exactly one head in the same situation? Two heads? Three heads?
What then is the probability of flipping -Four or more- heads in the same situation?
See Binomial Distribution on wikipedia.
How do the questions about coins I pose here relate to your original question?