How man different ways could a class of 20 line up single file in the hall?

Question

How man different ways could a class of 20 line up single file in the hall?

Answer 1

20!, meaning factorial 20, which equals 20*19*18*17*16 and so on down to 1.  It's a very large number.

In standard probability notation, it equals 20P20, meaning how many permutations are there of 20 things taken 20 at a time?  A permutation is a distinct ordering of the objects.

Answer 2

210 i think