Adding and Subtracting Integers

1
Adding and Subtracting Integers
Lesson 1.1.2
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Lesson 1.1.2
Adding and Subtracting Integers
California Standard Number Sense 2.3 Solve
addition, subtraction, multiplication, and
division problems, including those arising in
concrete situations, that use positive and
negative integers and combinations of these
operations.
What it means for you Youll learn to add
positive and negative numbers to integers.

• Key words
• positive
• negative
• integer

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Lesson 1.1.2
Adding and Subtracting Integers
Youve met positive and negative numbers, and you
know how to arrange them on the number line.
This Lesson covers addition and subtraction of
integers, including negative numbers.
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Lesson 1.1.2
Adding and Subtracting Integers
Adding a Positive Moves Right on the Number Line
In the last Lesson, you saw that numbers on the
number line are greater the farther to the right
they are.
When you add a positive integer to any number,
youre making it greater, so you move to the
right.
To add a positive integer, move that number of
positions to the right on the number line.
It doesnt make any difference whether the
original number is positive or negative you
always move to the right.
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Lesson 1.1.2
Adding and Subtracting Integers
Example 1
Using the number line, add 9 to 4.
Solution
Counting 9 spaces to the right of 4 on the
number line shows that the answer is 5.
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Adding a Negative Moves Left on the Number Line
When you add a negative integer, move that number
of positions to the left on the number line.
When youre adding a negative number, it doesnt
matter whether youre adding it to a positive or
negative number you always move to the left.
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Lesson 1.1.2
Adding and Subtracting Integers
Example 2
Using the number line, add 6 to 5.
Solution
Counting 6 spaces to the left of 5 on the number
line shows that the answer is 1.
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Example 3
Using the number line, add 5 to 1.
Solution
Counting 5 spaces to the left of 1 on the number
line shows that the answer is 6.
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Guided Practice
Answer the following Exercises without using a
calculator.Use a number line to help.
1. 7 3 2. 2 2 3. 8 4 4. 1 3
10
0
4
4
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Guided Practice
Answer the following Exercises without using a
calculator.Use a number line to help.
5. 81 8 6. 9 11 7. 9 (2) 8. 35 (10)
73
2
7
25
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Guided Practice
Answer the following Exercises without using a
calculator.Use a number line to help.
9. 5 (1) 10. 0 (5) 11. 36 (10) 12. 15
(7)
6
5
26
22
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Subtracting a Positive is Like Adding a Negative
You already know that to add a negative integer,
you move that number of positions to the left on
the number line.
The method for subtracting a positive integer is
exactly the same.
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Lesson 1.1.2
Adding and Subtracting Integers
Example 4
Using the number line, calculate 8 2.
Solution
The 2 tells you that you need to move 2 steps,
and the sign tells you that you need to move
left.
So the answer is 6.
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Guided Practice
Answer the following Exercises without using a
calculator.Use a number line to help.
13. 7 3 14. 1 10 15. 8 8
4
11
0
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Guided Practice
Answer the following Exercises without using a
calculator.Use a number line to help.
16. 3 8 17. 2 9 18. 1 10
5
11
9
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Subtracting a Negative Is Like Adding a Positive
Youve already seen that adding a negative means
you move left on the number line. So subtracting
a negative must mean you move right on the number
line.
Another way of saying this is that subtracting a
negative is the same as adding a positive.
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Lesson 1.1.2
Adding and Subtracting Integers
Example 5
Calculate 8 (3).
Solution
8 (3)
This sign tells you to go left on the number
line
but this sign reverses the direction again.
You end up moving 3 steps right on the number
line. So you can just write 8 (3) as 8 3
11.
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Guided Practice
Write Exercises 1924 as additions, then find the
solutions.
19. 14 (9) 20. 23 (10) 21. 9 (15) 22. 4
(4) 23. 4 (8) 24. 26 (17)
14 9 23
23 10 33
9 15 6
4 4 8
4 8 4
26 17 9
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Independent Practice
1. The water level of a lake in early April was 3
inches above normal. The water level had
dropped to 4 inches below normal by early May.
What integer can be added to 3 to get the water
level, in inches, in early May?
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Write each of Exercises 25 as an addition
problem. 2. 4 3 3. 7 8 4. 1 26 5. 4
5
4 (3)
7 (8)
1 (26)
4 (5)
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Independent Practice
Write each of Exercises 69 as a subtraction
problem. 6. 5 (9) 7. 1 (3) 8. 2 (1)
9. 433 (348)
5 9
1 3
2 1
433 348
Find the answer to each of Exercises 1013. 10. 4
(15) 11. 18 9 12. 23 6 13. 15
(3)
11
9
29
18
Solution follows
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Lesson 1.1.2
Adding and Subtracting Integers
Round Up
Adding to and subtracting from integers is a
matter of deciding which direction to move, then
moving the correct distance.
When youre deciding whether to go left or
rightyou only need to think about whether youre
adding a positive or negative number it doesnt
matter what youre adding it to.
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The Integer Song!

• Same signs add and keep.
• Different signs subtract.
• Take the sign of the higher number.
• Then youll be exact!

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Its Time For

• MATH SOCCER!!!
• Here are the rules