Forty dogs (all male) are placed in a box, yours, "Mr Froggy" is among them.

When the door is opened, one dog will come out at a time.

The winner, will be the second dog out.

What are the chances of Mr Froggy winning you the prize?

1/40th is the intuitive answer (each dog has an equal chance of being the second one out) and the mathematical one, as well. You're essentially betting on two events, so it is proper to multiply the probabilities of those events.

1. That he won't be the first one out.
2. That after another dog DOES come out, he'll be next.

You're a huge favorite on 1, and a huge underdog on 2. It's:

(39/40) (1/39) = 1/40 which, fortunately, is just what we expected!

There's no catching you guys out!