The number of ways in which 5 boys and 5 girls can be sit in a row so that all the girls sit together is

5 girls can be considered as one objects and 5 boys can be considered as five objects. Thus there are 6 objects. These six objects can be arranged in 6! ways. 5 girls can be permuted among themselves in 5! ways. Required number of arrangements = 6! x 5! =720 x 120 = 86400.