GED LESSON: Pre-Algebra: Adding and Subtracting Negative Numbers

ADDITION WITH NEGATIVE NUMBERS 


When adding numbers with the same signs (the signs of both numbers are positive or the signs of both numbers are negative),

Adding numbers with SAME SIGNS

1. Add the numbers
2. The answer keeps the same sign

For instance:      

         +2  +  +7  = +9
         -2  +  -7  = -9

When adding numbers with the different signs (if the first number is positive and the second number is negative, or the first number is negative and the second number is positive)

Adding numbers with DIFFERENT SIGNS

1. SUBTRACT the smaller number from the larger number regardless of signs)
2. Get the answer
3. Apply the sign of the larger number to the answer.

For instance:

         +2  +  -7  =  

          Step #1: Subtract the smaller number (2) from (7): 7 - 2 = 5 
          Step #2 The answer is 5
          Step #3 Since 7 is larger than 2 and 7 is negative, turn 5 into negative 5, so
       -5 is the answer. 

+2  +  -7  = -5

SUBTRACTION WITH NEGATIVE NUMBERS 

Subtraction is easy. Just change the sign of the SECOND number, then ADD using the additions rules above.

Examples:

Example one:           +2  -  -7  = +2  +  +7 = +9

Example two:           -2  -  +7  = -2  +  -7  = -9

Example three:               +2  -  +7  = +2  +  -7 = -5 

Example four:               -2  -  -7  = +2  +  +7 = +5 

FURTHER EXPLANATION AND PRACTICE CLICK HERE