1. Preview
Warm Up
California Standards
Lesson Presentation

2. Warm Up Simplify. 1. |–3| 3 2. –|4| –4
Write an improper fraction to represent each
mixed number. 2 14 3 6 55 7 3. 4 4. 7 3 7
Write a mixed number to represent each improper fraction. 12 2 5 24 2 3 5. 6. 5 9

3. California
Standards
2.0 Students understand and use such operations as taking the opposite, finding the reciprocal, taking a root, and raising to a fractional power. They understand and use the rules of exponents.

4. Vocabulary
real numbers
absolute value
opposites
additive inverse

5. The set of all numbers that can be represented on a number line are called real numbers. You can use a number line to model addition and subtraction of real numbers.
Addition
To model addition of a positive number, move right. To model addition of a negative number, move left.
Subtraction
To model subtraction of a positive number, move left. To model subtraction of a negative number, move right.

6. Additional Example 1A: Adding and Subtracting Numbers on a Number Line
Add or subtract using a number line.
–4 + (–7)
Start at 0. Move left to –4.
To add –7, move left 7 units.
+ (–7) –4 11 10 9 8 7 6 5 4 3 2 1
–4 + (–7) = –11

7. Additional Example 1B: Adding and Subtracting Numbers on a Number Line
Add or subtract using a number line.
3 – (–6)
Start at 0. Move right to 3.
To subtract –6, move right 6 units.
–(–6)
+ 3 -3 -2 -1 1 2 3 4 5 6 7 8 9
3 – (–6) = 9

8. -3 -2 -1 1 2 3 4 5 6 7 8 9 Check It Out! Example 1a
Add or subtract using a number line.
–3 + 7
Start at 0. Move left to –3.
To add 7, move right 7 units. +7 –3 -3 -2 -1 1 2 3 4 5 6 7 8 9
–3 + 7 = 4

9. Check It Out! Example 1b
Add or subtract using a number line.
–3 – 7
Start at 0. Move left to –3.
To subtract 7, move left 7 units. –7 –3 11 10 9 8 7 6 5 4 3 2 1
–3 – 7 = –10

10. Check It Out! Example 1c
Add or subtract using a number line.
Start at 0. Move left to –5.
–5 – (–6.5)
To subtract –6.5, move right 6.5 units.
– (–6.5) –5 8 7 6 5 4 3 2 1 1 2
–5 – (–6.5) = 1.5

11. The absolute value of a number is the distance from zero on a number line. The absolute value of 5 is written as |5|.
5 units
5 units - 6 - 5 - 4 - 3 - 2 - 1 1 2 3 4 5 6
|–5| = 5
|5| = 5

13. Additional Example 2: Adding Real Numbers
Different signs: subtract the
absolute values.
Use the sign of the number with the greater absolute value. B.
–6 + (–2)
(6 + 2 = 8)
Same signs: add the absolute values. –8
Both numbers are negative, so the sum is negative.

14. Check It Out! Example 2
Add. a.
–5 + (–7)
Same signs: add the absolute values.
(5 + 7 = 12)
–12
Both numbers are negative, so the sum is negative. b.
– (–22.3)
Same signs: add the absolute values.
( = 35.8)
Both numbers are negative, so the sum is negative.
–35.8

15. Check It Out! Example 2c
Add.
c (–68)
(68 – 52 = 16)
Different signs: subtract the
absolute values.
Use the sign of the number with the greater absolute value.
–16

16. Two numbers are opposites if their sum is 0
Two numbers are opposites if their sum is 0. A number and its opposite are additive inverses and are the same distance from zero. They have the same absolute value.

18. To subtract signed numbers, you can use additive inverses
To subtract signed numbers, you can use additive inverses. Subtracting a number is the same as adding the opposite of the number.

19. Subtracting Real Numbers

20. Additional Example 3A: Subtracting Real Numbers
–6.7 – 4.1
–6.7 – 4.1 = –6.7 + (–4.1)
To subtract 4.1, add –4.1.
( = 10.8)
Same signs: add absolute values.
–10.8
Both numbers are negative, so the sum is negative.

21. Additional Example 3B: Subtracting Real Numbers
5 – (–4)
5 − (–4) = 5 + 4
To subtract –4, add 4.
(5 + 4 = 9)
Same signs: add absolute values. 9
Both numbers are positive, so the sum is positive.

22. Additional Example 3C: Subtracting Real Numbers
To subtract
, add ,
Rewrite with a denominator
of 10.
Same signs: add absolute values .
Both numbers are negative, so the sum is negative.
–5.3

23. On many scientific and graphing calculators, there is one button to express the opposite of a number and a different button to express subtraction.
Helpful Hint

24. Check It Out! Example 3a
Subtract.
13 – 21
13 – 21
= 13 + (–21)
To subtract 21, add –21.
Different signs: subtract absolute values.
(21 – 13 = 8)
Use the sign of the number with the greater absolute value. –8

25. Check It Out! Example 3b
Subtract.
To subtract , add –3 1 2 3
Same signs: add absolute values.
Both numbers are positive, so the sum is positive. 4

26. Check It Out! Example 3c
Subtract.
–14 – (–12)
–14 – (–12) = –
To subtract –12, add 12.
(14 – 12 = 2)
Different signs: subtract absolute values. –2
Use the sign of the number with the greater absolute value.

27. Additional Example 4: Oceanography Application
An iceberg extends 75 feet above the sea. The bottom of the iceberg is at an elevation of
–247 feet. What is the height of the iceberg?
Find the difference in the elevations of the top of the iceberg and
the bottom of the iceberg.
elevation at bottom
of iceberg
elevation at top of iceberg
minus 75 –
–247
75 – (–247)
75 – (–247) =
To subtract –247, add 247.
Same signs: add the absolute values.
= 322

28. Additional Example 4 Continued
An iceberg extends 75 feet above the sea. The bottom of the iceberg is at an elevation of
–247 feet. What is the height of the iceberg?
The height of the iceberg is 322 feet.

29. elevation at top of iceberg
Check It Out! Example 4
What if…? The tallest known iceberg in the North Atlantic rose 550 feet above the ocean's surface. How many feet would it be from the top of the tallest iceberg to the wreckage of the Titanic, which is at an elevation of –12,468 feet?
elevation at top of iceberg
elevation of the
Titanic
minus –
550
–12,468
550 – (–12,468)
To subtract –12,468,
add 12,468.
550 – (–12,468) = ,468
= 13,018
Same signs: add the absolute values.

30. Check It Out! Example 4 Continued
What if…? The tallest known iceberg in the North Atlantic rose 550 feet above the ocean's surface. How many feet would it be from the top of the tallest iceberg to the wreckage of the Titanic, which is at an elevation of –12,468 feet?
Distance from the top of the iceberg to the Titanic is 13,018 feet.

31. Lesson Quiz
Add or subtract using a number line.
1. –2 + 9 7
2. –5 – (–3) –2
Add or subtract.
3. – 19
– (–3.7)
8.2 5.
6. The temperature at 6:00 A.M. was –23°F.
At 3:00 P.M., it was 18°F. Find the difference
in the temperatures.
41°F