A notorious postman delivered 4 letters to four houses in such a way that no house will get the correct letter.....in how many ways he delivered the letter??? please explain it please

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- Jun 17th 2013, 02:35 AMkashan123999Permutation Question
A notorious postman delivered 4 letters to four houses in such a way that no house will get the correct letter.....in how many ways he delivered the letter??? please explain it please

- Jun 17th 2013, 03:00 AMPlatoRe: Permutation Question
- Jun 17th 2013, 07:11 PMSorobanRe: Permutation Question
Hello, kashan123999!

Quote:

A notorious postman delivered 4 letters to four houses in such a way that no house got the correct letter.

In how many ways could he have delivered the letter?

The simplest way is to simplythe outcomes.*list*

Let the letters be

There are**9***derangements*of the four letters:

. .