Explanation
There are 6 distinct letters to pick from to fill the 1st slot. Then 6-1 = 5 letters for the next slot, and 6-2 = 4 letters for the last slot.
We have 6*5*4 = 120 different possible trios of letters. The order matters because an example like "KIN" is different from "INK".
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An alternative is to use the nPr formula with n = 6 and r = 3.
The nPr formula is [tex]_nP_r = \frac{n!}{(n-r)!}[/tex] where the exclamation marks indicate a factorial.
