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