Addition And Subtraction Of Signed Numbers

Adding and subtracting integers for the beginner seems very complicated at first glance. It just takes a little theory along with some good procedure. For starters, think opposite.

Adding With Different Signs

When we add two integers, we will subtract the two numbers and use the sign which number has the greatest amount.

Example:  (+3) + (-7)
We subtract, (7)  – (3).  
Then we ask ourself, which number is largest (+3 or -7)?
Obviously (-7)  is the largest number of the two.  Therefore, our answer will have a negative sign.
Answer is (-4)

Example: (-2) + (+8)
Same procedure here. 8 –  2  = 6. Look back at the problem. +8 was the larger number. So, the answer will be +6, or simply 6.

Example: (+6) + (-6)
Answer is 0

Subtracting With Different Signs

We will use a slightly different formula for subtraction, but we still do opposite. When we subtract integers, we always change the sign for the second number. Then we just add the numbers. (That’s opposite!)

Example: (-24) – (+9)
Okay, first thing we do is change the sign of the second number, which will be (-9). Then we add, (-24) + (-9)
Answer is (-33)

Example: (+4) – (-3)
This would become (+4) + (+3)
Answer is +7

Adding And Subtracting With Alike Signs

One last simple rule. Obviously, whether we add or subtract numbers with alike signs, we use the common sign.

Example: (+5) + (+3)
Answer is (+8)

Example: (-5) + (-2)
Answer is  (-7)

Example: (-7) – (-2)
Answer is  (-5)