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Mathematics 22 Online
OpenStudy (anonymous):

there are 7 letters and 7 envelopes . find the probability that no letter reaches its correct address???

Parth (parthkohli):

Hint: probability that no letter reaches the correct address = probability that all letters reach the wrong addresses.

OpenStudy (anonymous):

is it related to derangement ????

Parth (parthkohli):

Letter 1 has 6 ways it could go to a wrong place. Letter 2 has 5 ways because one letter has already been delivered. Letter 3 has 4. Letter 4 has 3. ... and so on

OpenStudy (anonymous):

Yes....Permutation and combination..u have to use this

OpenStudy (anonymous):

@ParthKohli then it will be like |dw:1346340930218:dw| is it right ???

OpenStudy (anonymous):

no....))

OpenStudy (anonymous):

|dw:1346340994607:dw|

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