You can put this solution on YOUR website!
Think of it this way...
How many ways can the first letter be written? Well, five ways...there are five different letter choices.
How many ways can the second letter be written? Well, since we only have four letters left (we used one already), there are only four possible choices.
Using the same logic, three are possible for the third, two for the fourth, and that leaves only one choice for the last letter...
So the answer turns out to be
5 * 4 * 3 * 2 * 1 = 120 possible ways.