In these lessons, we will look at adding integers and subtracting integers using the number line and using rules.
When we add, we move right on the number line.
When we subtract, we move left on the number line
To evaluate –3 + 2 , we start at –3 and move 2 places to the right
The answer is –1
To evaluate –3 – 2 , we start at –3 and move 2 places to the left
The answer is –5
Using the number line to add or subtract integers may be quite tedious. A quicker method would be to use the following rules:
Rule 1 :
The sum of two or more positive integers is a positive integer.
The sum of two or more negative integers is a negative integer.
(+7) + (+ 4) = + 11
(– 8) + (– 9) = – 17
Rule 2 :
To find the sum of a positive and a negative integer:
Subtract the two numbers (ignore the signs) and then keep the sign of the larger integer.
(– 9) + (+ 7) = – 2
(– 3) + (+ 5) = + 2
Rule 3 :
The sum of an integer and its opposite is equal to zero
(– 9) + (+ 9) = 0
(– 3) + (+ 3) = 0
To subtract integers, we can rewrite the subtraction problem as an addition problem. Instead of subtracting, we add the opposite.
3 − (4) = 3 + (−4)
3 − (− 4) = 3 + 4
We then follow the rules for adding integers.This video states the basic rules for subtracting integers and provides examples. Each subtraction problem is rewritten as an addition problem.
Subtracting Integers using Rules
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