In how many ways we can arrange $12$ people in a row if $5$ are men and they must sit next to each other?
My approach
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?
It makes sense to me. If there were only the 5 men present, there would be $5!$ choices. If there were 6 people present, the sixth person could sit either on the left side or the right, so $2! \times 5!$. And so on for $n$ total people, with $(n-4)!\times 5! .$ When $n=12$, we have $8!\times 5!$ different ways, as you say.