Find the number of ways of arranging 6 boys and 6 girls in row. In how many of these arrangements.
all the girls are together

Explanation

6 boys and 6 girls are altogether 12 persons. They can be arranged in a row in (12)! Ways.
Treat the 6 girls as one unit. Then we have 6 boys and 1 unit of girls. They can be arranged in 7! Ways. Now, the 6 girls can be arranged among themselves in 6! ways. Thus the number of ways in which all 6 girls are together is `(7! xx 6!)`.