7.8 adding positive and negative numbers
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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 + 5Pair and Cancel Method: Take nine negative tokens and five positive tokens
How do I add positive and negative numbers? Strategy #1
-9 + 5Pair a negative token with a positive token
How do I add positive and negative numbers?
-9 + 5The 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 + 6Pair and Cancel Method: Take nine negative tokens and five positive tokens
-3 + 6Pair 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 -1 0 1
Number Line Method
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 -1 0 1
Number Line Method
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 + 7Take three negative tokens and seven positive tokens
How do I add positive and negative numbers?
-3 + 7Pair a negative token with a positive token
How do I add positive and negative numbers?
-3 + 7The 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
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