How to Do Factorials

Step-by-Step Guide

1. 1

   Step 1: Determine the number you are computing the factorial for.

   A factorial is denoted by a positive integer and an exclamation point.
   
   For example, if you need to compute the factorial for 5, you will see 5!{\displaystyle 5!}.
2. 2

   Step 2: Write out the sequence of numbers to be multiplied.

   A factorial is simply multiplying the natural numbers that descend sequentially from the factorial number, down to
   1.Speaking formulaically, n!=n(n−1)⋅⋅⋅2⋅1{\displaystyle n!=n(n-1)\cdot \cdot \cdot 2\cdot 1}, where n{\displaystyle n} equals any positive integer.For example, if you are computing 5!{\displaystyle 5!}, you would compute 5(5−1)(5−2)(5−3)(5−4){\displaystyle 5(5-1)(5-2)(5-3)(5-4)} or, denoted more simply: 5⋅4⋅3⋅2⋅1{\displaystyle 5\cdot 4\cdot 3\cdot 2\cdot 1}. , You can compute a factorial quickly using a scientific calculator, which should have a x!{\displaystyle x!} sign.
   
   If you are computing by hand, to make it easier, first look for pairs of factors that multiply to equal
   10.Of course, you can also ignore the 1, since any number multiplied by 1 equals that number.
   
   For example, if computing 5!=5⋅4⋅3⋅2⋅1{\displaystyle 5!=5\cdot 4\cdot 3\cdot 2\cdot 1}, disregard the 1, and first calculate 5⋅2=10{\displaystyle 5\cdot 2=10}.
   
   Now all you are left with is 4⋅3=12{\displaystyle 4\cdot 3=12}.
   
   Since 10⋅12=120{\displaystyle 10\cdot 12=120}, you know that 5!=120{\displaystyle 5!=120}.
3. 3

   Step 3: Multiply the numbers together.

Detailed Guide

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