Six letters and six credit cards are to be placed into six corresponding envelopes. However, the letters and the credit cards are placed wrongly, so that none of the letters and none of the credit cards are placed correctly.
In how many different ways can this happen?
If the problem was asked for 3 letters, 3 credit cards and 3 envelopes, the answer would be 4.
Popularity: 53.6 %
Difficulty: 35.7 %