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2-1 Adding Integers
Pre-Algebra
Warm Up
Problem of the Day
Lesson Presentation
Warm UpGraph each number on a number line.
1. 5 2. 7
3. 4 4. 0
Pre-Algebra
2-1 Adding Integers
0 1 2 3 4 5 6 7 8 9 10
41 35Add.5. 22 + 19 6. 17 + 18
Problem of the Day
Start at (0, 0). Walk 3 blocks west and 2 blocks north. Then walk 4 blocks south and 1 block east. What are your coordinates?(–2, –2)
Pre-Algebra
2-1 Adding Integers
Learn to add integers.
Pre-Algebra
2-1 Adding Integers
Vocabulary
integer
opposite
absolute value
Insert Lesson Title Here
Pre-Algebra
2-1 Adding Integers
-5 -4 -3 -2 -1 0 1 2 3 4 5
Negative integers Positive integers
0 is its own opposite
–3 and 3 are opposites
Integers are sets of whole numbers, including 0, and their opposites. The sum of two opposite integers is zero.
Pre-Algebra
2-1 Adding Integers
To add a positive number move to the right. To add a negative number move to the left.
Helpful Hint
Additional Example 1: Using a Number Line to Add Integers
Use a number line to find the sum.
(–6) + 2
2
–6
You finish at –4, so (–6) + 2 = –4.
–6 –5 –4 –3 –2 –1 0 1 2 3 4 5
Pre-Algebra
2-1 Adding Integers
Try This: Example 1
Use a number line to find the sum.
(–3) + 7
7
–3
You finish at 4, so (–3) + 7 = 4.
–6 –5 –4 –3 –2 –1 0 1 2 3 4 5
Pre-Algebra
2-1 Adding Integers
Another way to add integers is to use absolute value. The absolute value of a number is its distance from 0. The absolute value of –4, written as |–4|, is 4; and the absolute value of 5 is 5.
Adding integers
If the signs are the same. . . If the signs are different. . .
find the sum of the absolute values. Use the same sign as the integers.
find the difference of the absolute values. Use the sign of the integer with the larger absolute value.
Pre-Algebra
2-1 Adding Integers
Additional Example 2A & 2B: Using Absolute Value to Add Integers
A. 1 + (–2)
Think: Find the difference of 2 and 1.
Add.
1 + (–2)
2 > 1; use the sign of 2. –1
B. (–8) + 5
Think: Find the difference of 8 and 5. (–8) + 5
8 > 5; use the sign of 8. –3
Pre-Algebra
2-1 Adding Integers
Additional Example 2C: Using Absolute Value to Add Integers
C. (–2) + (–4)
Think: Find the sum of 2 and 4.
Add.
(–2) + (–4)
Same sign; use the sign of the integers. –6
Pre-Algebra
2-1 Adding Integers
Try This: Example 2A & 2B
A. 3 + (–6)
Think: Find the difference of 6 and 3.
Add.
3 + (–6)
6 > 3; use the sign of 6. –3
B. (–4) + 1
Think: Find the difference of 4 and 1. (–4) + 1
4 > 1; use the sign of 4. –3
Pre-Algebra
2-1 Adding Integers
Try This: Example 2C
C. (–6) + (–7)
Think: Find the sum of 6 and 7.
Add.
(–6) + (–7)
Same sign; use the sign of the integers. –13
Pre-Algebra
2-1 Adding Integers
Additional Example 3: Evaluating Expressions with Integers
Evaluate c + 4 for c = –8.
c + 4
Replace c with –8.Think: Find the difference of 8 and 4.
8 > 4; use the sign of 8.
(–8) + 4
–8 + 4 = –4
Pre-Algebra
2-1 Adding Integers
Try This: Example 3
Evaluate d + 7 for d = –3.
d + 7
Replace d with –3.Think: Find the difference of 7 and 3.
7 > 3; use the sign of 7.
(–3) + 7
–3 + 7 = 4
Pre-Algebra
2-1 Adding Integers
Additional Example 4: Application
Katrina opened a new bank account. Find her account balance after the first four transactions listed below.
Deposits: $200, $20 Withdrawals: $166, $38
Use a positive sign for deposits and a negative sign for withdrawals.
200 + 20 + (–166) + (–38)
Group integers with same signs.(200 + 20) + (–166 + –38)
Add integers within each group.220 + (–204)
220 > 204; use the sign of 220.16
Katrina’s account balance after the first four transactions is $16.
Pre-Algebra
2-1 Adding Integers
Try This: Example 4
Michael opened a new bank account. Find his account balance after the first four transactions listed below.
Deposits: $175, $95 Withdrawals: $133, $65
Use a positive sign for deposits and a negative sign for withdrawals.
175 + 95 + (–133) + (–65)
Group integers with same signs.(175 + 95) + (–133 + –65)
Add integers within each group.270 + (–198)
270 > 198; use the sign of 270.72
Michael’s account balance after the first four transactions is $72.
Pre-Algebra
2-1 Adding Integers
Lesson Quiz: Part 1
Add.
1. –7 + (– 7)
2. 15 + (–9) + (–2)
4
–14
Insert Lesson Title Here
Evaluate each expression for the given
value of the variable.
3. 13 + r for r = –15
4. 2 + b + (–9) for b = –6
–2
–13
Pre-Algebra
2-1 Adding Integers
Lesson Quiz: Part 2
5. On Monday, a local dog shelter had six dogs.
By Friday they had found homes for three, but
took in two more. Then how many dogs were in
the shelter?
Insert Lesson Title Here
5 dogs
Pre-Algebra
2-1 Adding Integers
