You type four letters to four different people and address the envelopes. If you then insert the letters into the envelopes randomly, what is the probability that exactly three letters will go into the correct envelopes?

Answer 1

I think this is trick question.
If 3 are correct, how can the fourth be wrong?

So all 4 will have to be right.
prob of that = 1/4! = 1/24

Answer 2

Exactly 3 is impossible. If 3 were right, 4 would have to be right. The chances of exactly 3 would be 0.