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Factorial Notation

When you see an exclamation mark following a number in mathematics it is known as a factorial. For example, 6! is said ‘6 factorial’ and you multiply all of the positive integers less than 6 together:

6!=6\times 5\times 4 \times 3 \times 2 \times 1=720

Here are some more examples:

8!=8\times 7\times 6\times 5\times 4 \times 3 \times 2 \times 1=40,320

4!\times 3!=4\times 3\times 2 \times 1\times 3\times 2 \times 1=24\times 6=144

9!\div 5!=\frac{9\times 8\times 7\times 6\times 5\times 4 \times 3 \times 2 \times 1}{5\times 4 \times 3 \times 2 \times 1}=9\times 8\times 7\times 6=3,024