Permutations And Combinations Question 184

Question: There are four letters and four directed envelopers. The number of ways in which all the letters can be put I the wrong envelope is

Options:

A) 8

B) 9

C) 16

D) none of these

Show Answer

Answer:

Correct Answer: B

Solution:

  • [b] There is concept of derangement. The require number is $ 4![ 1-\frac{1}{1!}+\frac{1}{2!}-\frac{1}{3!}+\frac{1}{4!} ]=9 $

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