Find the number of ways in which 4 letters can be put in 4 addressed envelopes so that no letter goes into the envelope meant for it.

The number of ways in which four letters can be put in four addressed envelops so that no letter goes into envelope meant for it is

The number of ways in which 5 letters can be placed in 5 marked envelopes, so that no letter is in the right encelope, is

The number of ways in which 5 letters can be placed in 5 marked envelopes, so that no letter is in the right encelope, is

There are 3 letters and 3 addressed envelopes coorresponding to their . The number of ways in which the letters be placed in the envelopes so that no letter is in the right envelope is

The number of ways in which four different letters can be put in their four addressed envelopes that

The number of ways in which four different letters can be put in their four addressed envelopes that

If the number of ways in which 7 letters can be put in 7 envelopes such that exactly four letters are in wrong envelopes is N, then

If the number of ways in which 7 letters can be put in 7 envelopes such that exactly four letters are in wrong envelopes is N, then