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

There are seven even greeting cards each of a different colour and seven envelopes of the same seven colours. Find the number of ways in which the cards can be put in the envelopes so that exactly four of the cards go into the envelopes of the right colour.

Ravish writes letters to his five friends and addresses the correspondig envelopes.The total number of ways in which letters can be placed in the envelopes so that at least two of them are in the wrong envelopes,is

Ravish writes letters to his five friends and addresses the correspondig envelopes. The total number of ways in which letters can be placed in the envelopes so that at least two of them are in the wrong envelopes, 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

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.

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