Question

It is required to seat 5 men and 4 women in a row so that the women occupy the even places. How many such arrangements are possible ?

Answer 1

The arrangement will be MWMWMWMWM 
1 2 3 4 5 6 7 8 9 
Women could occupy even places 2,4,6,8 in 4! ways. 

The 5 mean can occupy the 5 odd places in 5! ways. 
Total number of ways = 4! 5! = (24)(120) = 2,880