Teaching Notes 1.15: Adding Integers with Different Signs
Adding two integers with different signs may seem like subtraction of integers to some students.
They do not realize that when adding a positive integer and a negative integer, the negative
integer ‘‘negates’’ the value of the positive integer.- Ask your students to imagine that a student gained 50 points while playing a video game and
then lost 10 points. Explain that the loss of 10 points negates 10 of the 50-point gain. The
student now has only 40 points. The 10-point loss can be represented by−10. - Explain that this situation can be modeled by adding integers. 50+(−10)=40. The process
is addition because the student gained 50andlost 10. The word ‘‘and’’ indicates addition. - Now ask your students to suppose that another student lost 40 points and gained 30 in a
video game. The 40-point loss has gained 30 more points, resulting in only a 10-point loss.
This can also be modeled by adding integers.− 40 + 30 =− 10 - Review the rules and examples for adding integers on the worksheet with your students.
EXTRA HELP:
Positive symbols for numbers can be omitted as a number without a sign is assumed to be positive.
Negative signs must always be included.ANSWER KEY:
(1) 17 (2) 9 (3) 0 (4)− 8 (5)− 7 (6)− 24 (7) 62 (8) 49 (9) 5 (10)− 25 (11) 14 (12)− 12
------------------------------------------------------------------------------------------
(Challenge)Answers may vary. One acceptable response is− 10 + 3 =−7and5+(−4)=1.
------------------------------------------------------------------------------------------30 THE ALGEBRA TEACHER’S GUIDE