5P3 = 5*4*3 = 60

Start with the first number, and start multiplying by 1 less each time
until you have the second number of factors.  Then multiply.

We started with 5, then multiplied by 1 less, or 4, then by 1 less than
that, 3. So we had 5*4*3. We stopped there because we had 3 factors.
Then we multiplied them and got 60.  

Edwin