## Question

A person writes 4 letters and addresses on 4 envelopes. If the letters are placed in the envelopes at random, the probability that not all letters are placed in correct envelopes is

### Solution

23/24

Required probability

= 1 – *P* (all the letters are put is correct envelops)

The numbers of ways of putting the letters in the envelops

The number of ways of putting letters in correct envelops = 1

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