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In how many ways can 4 different letters be placed in 4 addressed envelopes (one letter in each envelope) so that no letter is placed in it…

2303Medium DSSSB TGT Computer Science 0 replies 1 views
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In how many ways can 4 different letters be placed in 4 addressed envelopes (one letter in each envelope) so that no letter is placed in its own envelope?

  • A9
  • B8
  • C12
  • D6
Correct answer: A

Explanation

The number of derangements of 4 objects is 24 − 24 + 12 − 4 + 1 = 9.

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