Question

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

• A. $8$
• B. $9$
• C. $16$
• D. None of these

Answer 1

Answer: (B)

$9$

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