Download How do I add positive and negative numbers?

7.8 Adding Positive and
Negative Numbers
Miss Hepner
Math Message
Mental Math Reflexes
Use <, >, or = to compare numbers
1. -5 and -7
2. 2.5 and -1
3. - 8/4 and -2
Adding Positive and Negative
Numbers
• Objective: To develop rules for adding positive
and negative numbers
• Lesson Essential Question: How do I add
positive and negative numbers and what
strategy can I use?
3 Strategies
• Today we will learn 3 different strategies to add
positive and negative numbers. You choose
the strategy that works best for you!
The three strategies include:
1. Pair and cancel (using + and – tokens)
2. Number line method
3. Subtract and Highest Sign (team and battle)
How do I add positive and
negative numbers? Strategy #1
-9 + 5
Pair and Cancel Method: Take nine negative tokens and
five positive tokens
How do I add positive and
negative numbers? Strategy #1
-9 + 5
Pair a negative token with a positive token
How do I add positive and
negative numbers?
-9 + 5
The paired tokens cancel each other out!
Count the left over tokens and there is your answer.
How do I add positive and
negative numbers?
-9 + 5 = -4
Let’s try another example using
Strategy #1
-3 + 6
Pair and Cancel Method: Take nine negative tokens and
five positive tokens
-3 + 6
Pair a negative token with a positive token
Count your left over
tokens and that is
your answer.
How do I add positive and
negative numbers?
-3 + 6 = 3
Another way to look at it:
-9 + 5
-9
-8
-7
-6
-5
-4
-3
-2
Number Line Method
-1
0
1
Another way to look at it:
-9 + 5 = -4
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
Strategy #2- Number Line
-5 + -3
-9
-8
-7
-6
-5
-4
-3
-2
Number Line Method
-1
0
1
Strategy #2- Number Line
-5 + -3 = -8
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
Another way to think about it…
• Subtract the two number and take the sign of
the larger:
-9 + 5 =
9 – 5 = 4 (take the sign of the larger)
Answer = -4
Subtract and Highest Sign Method
Pair and Cancel Method
-3 + 7
Take three negative tokens and seven positive tokens
How do I add positive and
negative numbers?
-3 + 7
Pair a negative token with a positive token
How do I add positive and
negative numbers?
-3 + 7
The paired tokens cancel each other out!
Count the left over tokens and there is your answer.
How do I add positive and
negative numbers?
-3 + 7 = 4
Number Line Method
-3 + 7
-3
-2
-1
0
1
2
3
4
5
6
7
Another way to look at it:
-3 + 7 = 4
-3
-2
-1
0
1
2
3
4
5
6
7
Subtract and Highest Sign Method
• Subtract the two number and take the sign of
the larger:
-3 + 7 =
-3 + 7 = 4 (take the sign of the larger)
Answer = 4
Practice:
• 7 – 10
• -4 + 12
• 9 – 15
• -3 + 8
• -6x + 2x