6 friends go to a party, each one carrying a different umbrella. They place the umbrellas outside. When the party is over, they are drunk and each one grabs an umbrella at random. In how many ways could none of them have taken the right umbrella? I'm having a bit trouble with this, as I can't seem to solve it without having to do some rough counting some times. Can any of you bother to solve this and explain it to me?