This is a question of permutation. There are only 3 ways. A-B-C, B-C-A, C-A-B
There are 5040 ways.
7
20*19*18*17*16 = 1860480 ways.
for the first student in the line there are 10 choices, then for the second 9 choices left, for the third 8 choices left and so on... So it's 10x9x8x7x6x5x4x3x2x1 = 3628800
720
3 items (or people) can line up in 6 different sequences. 6 items (or people) can line up in 720 different sequences.
6 = 3*2*1
5x4x3x2x1=120
25
If you keep them in a line, there are 24 ways to line them up. Then of course there are squares, diamonds, rectangles, parallelograms, stacks, etc.
27!
302 i think not to sure though