# Numerical Operations

A numerical operation can be described as an action or process used to solved a numerical problem.

If you have two numbers x and y, the following rules apply when these numbers are being added or subtracted.

• Rule of Signs for Addition:   (xy) is the same as x + (–y)  or  x – (+y) because a negative beside a positive (or vice versa) always make a negative.
• Rule of Signs for Subtraction:   x + y is the same as x – (–y) because two negatives side-by-side make a positive.

Here are a few examples:

null

For #1, the answer is clearly 9. But you could also have gotten 9 if you had:   7  (2) because of the rule of signs for subtraction.

For #2, the answer is 5. But you could also have gotten 5 if you had:   9 + (–4) or 9 – (+4) because of the rule of signs for addition.

For #3, the answer is –2.

A summary of these symbols is shown below:

null

More examples: null

#1:   14

#2:  –2

#3:   18

[collapse]

Multiplying and Dividing Signed Numbers

• Rules of Signs for Multiplication:
• (+x)(+y) = (–x)(–y) = +xy
• (+x)(–y) = (–x)(+y) = –xy
• It’s also important to note that the same rules apply for division too.

Multiplication of two or more factors can be symbolized in 3 main ways:

null

For division:

null

Here are a few examples:

null