Probability brain teaser of secret santa

Asked Dec 03 '15 at 21:20

Active Dec 03 '15 at 21:41

Viewed 54 times

There is a room having 100 people. There is a box with letters containing names of 100 people on it. No two people have same name. Everyone is supposed to pick one letter and keep it.

What is the probability that someone will pick the letter with his own name?

asked Dec 03 '15 at 21:20

pg2455

4

Hello and welcome to Math SE. It is customary to post work you have done so we can help you with any difficulties you have. – Kevin Zakka Dec 03 '15 at 21:24
2

Hint: P(at least one finds his own letter) = 1 - P(nobody finds their own letter) – Marcus Andrews Dec 03 '15 at 21:27
Such problems have been posted many times here. An early example is Number of permutations of $n$ where no number $i$ is in position $i$. I will vote to close as duplicate some more recent post whose answers go into more computational detail. – hardmath Dec 03 '15 at 21:34

Probability brain teaser of secret santa

0 Answers0