Possibilities

[sexy offline]

In how many ways can seven customers form a single line to purchase a ticket at a ticket booth. That is how many different lines of seven people are possible

[admin]

7!

first customer can be placed at 7 different positions in the line.

second customer can be placed at (7-1)=6 different positions in the line. (because first customer already occupies a position).

and so on.

that's: 7 (possibilities first customer) * 6(possibilities second customer) * 5*4*3*2 * 1 (possibility last customer) = 1*2*3*4*5*6*7 = 7!