30.In how many ways can 4 girls and 5 boys be arranged in a row so that all the four girls are together?
Solution:
Let 4 girls be one unit and now there are 6 units in all.
They can be arranged in 6! ways.
In each of these arrangements 4 girls can be arranged in 4! ways.
=> Total number of arrangements in which girls are always together
=6!*4!=720*24= 17280
