# Adding and Subtracting Integers or Whole Numbers

- - Pre-Algebra

Adding and subtracting integers or whole numbers need the understanding of positive and negative integers. From your previous experience in arithmetic you are aware of the necessity for a system of numbers which will denote direction as well as amount. Thus, if +3 indicates 3 units to the right on a number scale, -3 indicates 3 units to the left.

Numbers that tell us which way as well as how much or how many are called signed numbers.

A signed number preceded by a plus (+) sign is called a positive number; if it is preceded by a minus (-) sign, it is called a negative number. If no sign is expressed, the number is considered to be positive.

The value of a number without regard to its sign is called its absolute value.

Rules of Adding and Subtracting Whole Numbers or Integers

• To add two numbers having like signs, find the sum of their absolute values and prefix the common sign.
• To add two numbers having unlike signs, find the difference of their absolute values and prefix the sign of the greater number.
Subtraction:
• Mentally change the sign of the subtrahend and proceed as in arithmetic addition.
Examples: Find each sum.
1. (-10) + 6 = -4
2. (-9) + (-5) = -14
3. (-3) + 15 = 12
4. 10 + 5 = 15
5. 2 +12 = 14
Examples: Find each difference.
1. 3 − (-4) = 3 + 4 = 7
2. (-3) − 20 = (-3) + (-20) = -23
3. 9 − 4 = 5
4. (-7) − (-6) = (-7) + 6 = -1
5. 10 − 2 = 8
Examples: Evaluate each expression.
1. (-20) − 24 = (-20) + (-24) = -44
2. (-10) + (-20) = -30
3. 3 + 5 + 14 = 22
4. 26 + (-10) + 5 = 21
5. 1 − (-10) − 8 = 1 + 10 − 8 =  3