Hands-on math!

Factorial

A factorial is a number that is the result of multiplying a number by all the whole numbers below it. It is written with an exclamation mark (!) after it, like this:
5!

Here are two examples:
5! =       5 x 4 x 3 x 2 x 1 = 120
6! = 6 x 5 x 4 x 3 x 2 x 1 = 720

Notice that if you divide 6! by 5! you get only the 6: 

6! = 6 x 5 x 4 x 3 x 2 x 1
-------------------------- = 6
5! =     5 x 4 x 3 x 2 x 1
... because all the numbers in 5! cancel the same numbers in 6! Now here are a couple of problems for you:

What is 4!? _________

What is 5! / 2! ? __________