1. Adding and Subtracting Decimals
3-3
Adding and Subtracting Decimals
Course 1
Warm Up
Problem of the Day
Lesson Presentation

2. Adding and Subtracting Decimals
Course 1
3-3
Adding and Subtracting Decimals
Warm Up
Estimate by rounding to the indicated place value.
; ones
– 21.82; tenths
Estimate each product or quotient.
 8.7
÷ 3.27 85
62.6
270 15

3. Adding and Subtracting Decimals
Course 1
3-3
Adding and Subtracting Decimals
Learn to add and subtract decimals.

4. Adding and Subtracting Decimals
Course 1
3-3
Adding and Subtracting Decimals
Estimating before you add or subtract will help you check whether your answer is reasonable.
Helpful Hint

5. Carly Patterson’s Preliminary Scores
Course 1
3-3
Adding and Subtracting Decimals
At the 2004 U.S. Gymnastics Championships, Carly Patterson and Courtney Kupets tied for the All-Around title.
Carly Patterson’s Preliminary Scores
Event
Points
Floor exercise
9.7
Balance beam
Vault
9.3
Uneven bars
9.45
To find the total number of points, you add all of the scores.

6. Additional Example 1A: Sports Application
Course 1
3-3
Adding and Subtracting Decimals
Additional Example 1A: Sports Application
What was Carly Patterson’s total for the events other than the floor exercise?
Find the sum of 9.7, 9.3, and 9.45.
Estimate by rounding to the nearest whole number.
The total is about 28 points.
= 28

7. Additional Example 1A Continued
Course 1
3-3
Adding and Subtracting Decimals
Additional Example 1A Continued
Add.
Align the decimal points.
9.70
Use zeros as placeholders.
9.30
+9.45
Add. Then place the decimal point.
28.45
Since is close to the estimate of 28, the answer is reasonable. Carly Patterson’s total for the events other than the floor exercise was

8. Additional Example 1B: Sports Application
Course 1
3-3
Adding and Subtracting Decimals
Additional Example 1B: Sports Application
How many more points did Carly need on the vault to have a perfect score of 10?
Find the difference between 10 and 9.3.
Align the decimal points.
10.0
Use zeros as placeholders.
-9.3
0.7
Subtract. Then place the decimal point.
Carly needed another 0.7 of a point to have a perfect score.

9. Adding and Subtracting Decimals
Course 1
3-3
Adding and Subtracting Decimals
Check It Out: Example 1A
What was Carly Patterson’s total for the events other than the vault exercise?
Find the sum of 9.7, 9.7, and 9.45.
Estimate by rounding to the nearest whole number.
The total is about 29 points.
= 29

10. Check It Out: Example 1A Continued
Course 1
3-3
Adding and Subtracting Decimals
Check It Out: Example 1A Continued
Add
Align the decimal points.
9.700
Use zeros as placeholders.
9.700
+9.450
Add. Then place the decimal point.
28.850
Since is close to the estimate of 29, the answer is reasonable. Carly Patterson’s total for the events other than the vault exercise was

11. Adding and Subtracting Decimals
Course 1
3-3
Adding and Subtracting Decimals
Check It Out: Example 1B
How many more points did Carly need on the uneven bars to have a perfect score of 10?
Find the difference between 10 and 9.45.
Align the decimal points.
10.00
Use zeros as placeholders.
-9.45
0.55
Subtract. Then place the decimal point.
Carly needed another 0.55 of a point to have a perfect score.

12. Additional Example 2: Using Mental Math to Add and Subtract Decimals
Course 1
3-3
Adding and Subtracting Decimals
Additional Example 2: Using Mental Math to Add and Subtract Decimals
Find each sum or difference. A
B. 4 – 0.7
2.0
4 – 0.7
3.3

13. Adding and Subtracting Decimals
Course 1
3-3
Adding and Subtracting Decimals
Check It Out: Example 2
Find each sum or difference. A
B. 6 – 0.3
2.0
6 – 0.3
5.7

14. Additional Example 3A: Evaluating Decimal Expressions
Course 1
3-3
Adding and Subtracting Decimals
Additional Example 3A: Evaluating Decimal Expressions
Evaluate 6.73 – x for each value of x.
x = 3.8
6.73 – x
Substitute 3.8 for x.
6.73 – 3.8
6.73
Align the decimal points.
Use a zero as a placeholder.
– 3.80
Subtract. Place the decimal point.
2.93

15. Adding and Subtracting Decimals
Course 1
3-3
Adding and Subtracting Decimals
You can place any number of zeros at the
end of a decimal number without changing
its value.
Helpful Hint

16. Additional Example 3B: Evaluating Decimal Expressions
Course 1
3-3
Adding and Subtracting Decimals
Additional Example 3B: Evaluating Decimal Expressions
Evaluate 6.73 – x for each value of x.
x =
6.73 – x
Substitute for x.
6.73 –
3.7535

17. Adding and Subtracting Decimals
Course 1
3-3
Adding and Subtracting Decimals
Check It Out: Example 3A
Evaluate 7.58 – x for each value of x.
x = 3.8
7.58 – x
Substitute 3.8 for x.
7.58 – 3.8
3.78
Subtract.

18. Adding and Subtracting Decimals
Course 1
3-3
Adding and Subtracting Decimals
Check It Out: Example 3B
Evaluate 8.17 – x for each value of x.
x =
8.17 – x
Substitute for x.
8.17 –
5.1935
Subtract. .

19. Adding and Subtracting Decimals Insert Lesson Title Here
Course 1
3-3
Adding and Subtracting Decimals
Insert Lesson Title Here
Lesson Quiz
Find each sum or difference.
– 4
4. Evaluate – x for x = 8.41.
5. During an ice-skating competition, Dawn received the following scores: 4.8, 5.2, 5.4. What was Dawn’s total score? 11
5.7 31
4.35
15.4