1. The problem statement, all variables and given/known data Six cards and six envelopes are numbered 1,2,3,4,5,6 and cards are to be placed in envelopes so that each envelope contains exactly one card and no card is placed in the envelope bearing the same number and moreover the card numbered 1 is always placed in envelope numbered 2. Then the number of ways it can be done is 264 265 53 67 2. Relevant equations There are many permutations formulas. Some say to learn it not telling the reason behind it. 3. The attempt at a solution I think here some formula is applicable of degenerate theorem of permutation but what is the intuition behind it? It is better to analyse a formula before applying it anywhere.