Wrong envelop
Probability
Level
pending
A correspondent prepared 7 letters and 7 envelopes with different addresses, one for each letter. In how many ways, all the 7 letters could be placed in wrong envelopes?
42
1854
5030
124
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1 solution
Number of derangement for n objects d(n) = (n-1) ( d(n-1) + d(n-2) )
d(7) = 6 ( 265 + 44 ) = 1,854