No two men together...

How many ways can 4 men and 4 women sit in a row of 8 seats such that no two men sit together?

Assume that all people are distinguishable. So if Fred and Ted switch places, it's a different formation.


The answer is 2880.

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2 solutions

Aaghaz Mahajan
Jun 24, 2019

First seat all the males. This can be done in 4 ! = 24 \displaystyle 4!=24 ways. Now, observe that there are 3 gaps between the 4 men (excluding the empty gaps at the left and right side of the leftmost and the rightmost men). So, we need to fill these with 3 women out of the 4. This again can be done in 4 ! = 24 \displaystyle 4!=24 ways. Finally, the last woman can now be place in any of the 5 remaining gaps (now, including the before excluded empty gaps).

So, the final answer is 4 ! 2 5 = 2880 \displaystyle 4!^2\cdot5=2880

Geoff Pilling
Jun 24, 2019

There are 5 patterns:

  • mwmwmwmw
  • wmwmwmwm
  • mwwmwmwm
  • mwmwwmwm
  • mwmwmwwm

And there are 4 ! = 24 4! = 24 ways each sex can arrange themselves within each pattern.

So there are 5 24 24 = 2880 5\cdot24\cdot24 = 2880 ways all together.

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