How many ways are there for 8 men and 5 women to stand in a line so that no two women stand next to each other? I have a homework problem in my textbook that has stumped me so far. There is a similar one to it that has not been assigned and has an answer in the back of the textbook. It reads: 
How many ways are there for $8$ men and $5$ women to stand in a line so that no two women stand next to each other?
The answer is $609638400$, but no matter what I try I cannot reach that number. I have tried doing $2(8!5!/3!)*(8!/5!)$ since each woman must be paired with a man in order to prevent two women getting near each other. But of course, it's the wrong answer. 
What am I doing wrong here?

*

*M * M * M * M * M * M * M * M * .


there are 9 "*" .
8 "M"  .
now select 5 * from 9 * then == c(9,5)
