Question 173322
There are 5 ways to choose the first tile.  For each of those 5 ways to choose the first tile, there are 4 ways to choose the second tile.  For each of those 20 ways ( 5 X 4 ) to choose the first two tiles, there are 3 ways to choose the third, and so on.


So:  5 X 4 X 3 X 2 X 1 = 120


Mathematicians abbreviate this as 5!, read 5 factorial.