In how many ways can 6 graduates line up to receive their diplomas, if there are 4 girls and 2 boys and the girls will receive their diplomas first?
this corresponds to how many ways girls can line up and then for each of these ways how we can include the boys lined up. Lets Consider how many ways can 2 people line up...
if there are 3 people
in fact this pattern will repeat in the following ways
so when the girls line up they will line up
when only the boys line up they will do so in
so girls can line up