A soccer team consists of five girls and four boys. (All the players are distinguishable.) How many ways can they stand in line for a photograph, so that at least two of the girls are standing next to each other?
First we want to count the number cases without any restriction which is 9! Then we count the number we don't want which is 5*4*4*3*3*2*2*1*1 = 2880. 9!-2880 = 360000.
