My probability is too foggy to work out the expected number of rides he would have to take to have a 50% (or 90%) chance of riding on each of the 32 cars.

I am assuming that it is a very large number (thousands?).

Can anyone supply the formula f(

*N*,

*P*) where

*N*is the number of cars and

*P*is the target probability (50%, 90%)?

Thanks