The first one on the list can be any one of 25.
For each of those . . . . .
The 2nd one on the list can be any one of the other 14.
For each of those . . . . .
The 3rd one can be any one of the other 13.
.
.
.
The total number of different ways to list them is "15 factorial" .
That's written as " 15 ! ". It means
15 · 14 · 13 · 12 · 11 · 10 · 9 · 8 · 7 · 6 · 5 · 4 · 3 · 2 · 1
and it's a big number.
15 ! = 1,307,674,368,000 (rounded to the nearest thousand).
