Permutations And Combinations Question 25

Question: $ m $ men and n women are to be seated in a row so that no two women sit together. If $ m>n $ , then the number of ways in which they can be seated is [IIT 1983]

Options:

A) $ \frac{m\ !\ (m+1)\ !}{(m-n+1)\ !} $

B) $ \frac{m\ !\ (m-1)\ !}{(m-n+1)\ !} $

C) $ \frac{(m-1)\ !\ (m+1)\ !}{(m-n+1)\ !} $

D) None of these

Show Answer

Answer:

Correct Answer: A

Solution:

  • First arrange m men, in a row in m! ways. Since $ n<m $ and no two women can sit together, in any one of the $ m! $ arrangement, there are $ (m+1) $ places in which n women can be arranged in $ ^{m+1}P _{n} $ ways.
    $ \therefore $ By the fundamental theorem, the required number of arrangements of m men and n women $ (n<m) $ = $ m!{{.}^{m+1}}P _{n}=\frac{m!.(m+1)!}{{(m+1)-n}!}=\frac{m!(m+1)!}{(m-n+1)!} $ .