In how many ways we can arrange $12$ people in a row if $5$ are men and they must sit next to each other?
I consider $5$ men as one entity and so now there are $8$ people to be seated in a row, which is done in 8! ways. The $5 $ men considered as one entity can themselves be seated in $5!$ ways. So the total number of ways are $8!5!$ (multiplication rule). What's wrong with the approach?