Question

How many three-letter "words" can be made from 5 letters "FGHIJ" if repetition of letters

Answer 1

So basically you just want to say:

5 choices, with five choices stemming from that, with five more choices stemming from that.

(Drawing a tree would show that well)

Or, 

5 * 5 * 5

Which is,

25 * 5

Or 125.

So 125 three letter words can be made from the letter FGHIJ