If five girls and five boys stand in a circle, how many arrangements are possible provided they stand alternately (girl, boy, girl, boy, etc)?
This is circular permutation
5 boys can stand in a circle in (5-1)!=4! ways
there are 5 gaps in between 5 boys and 5 girls can stand in those gaps in 5! ways
so total number of arrangements=4!*5!=24*120=2880