1. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
Do Now
Estimate by rounding to the nearest integer.
(–8.23)
– 3.16 8 –1 6 18
Hwk: p 25, 26

2. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
Problem of the Day
Complete the magic square. The sum of each row, column, and diagonal must be the same number.
0.5 7
4.625
8.75
6.375
5.25 4
2.25
2.875

3. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
EQ: How do I add/subtract/multiply/divide decimals?
M7N1.c Add, subtract, multiply, and divide positive and negative rational numbers

4. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
Add 66.8 and 4
66.8
+ 4.0
Use zero as a placeholder so that
both numbers have the same number
of digits after their decimal points.
70.8
Add each column just as you would
add integers.
Line up the decimal points.

5. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
4.55
15.85
Estimate
= 16

6. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
6.44
22.44
Estimate
= 22

7. Insert Lesson Title Here
Course 2
3-2
Adding and Subtracting Decimals
Insert Lesson Title Here
When adding numbers with the same sign, find the sum of their absolute values. Then use the sign of the numbers.
Remember!

8. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
– (–10.972)
Estimate
–8 + (–11) = –19

9. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
19.98
Estimate
= 20

10. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
38.21
Estimate
= 38

11. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
– (–13.852)
= –21.742
Estimate
–8 + (–14) = –22

12. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
A – 2.08
3.26
B. 28 –
28.000
–15.911
12.089

13. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
A – 1.46
2.11
B. 34 –
34.000
–12.462
21.538

14. Adding and Subtracting Decimals
Course 2
3-2
Adding and Subtracting Decimals
During one month in the United States,
million commuter trips were taken on buses,
and million commuter trips were taken
on light rail. What was the total number of trips
taken on buses and light rail?
The total number of trips was million.

15. Insert Lesson Title Here
Course 2
3-2
Adding and Subtracting Decimals
Insert Lesson Title Here
In 1999, million bushels of corn were
grown in the United States. In 2000, the harvest
yielded million bushels. What was the
total production for those two years?
The total number of bushels was million.

16. 7  8 56 0.7  0.8 0. 56 3-3 Multiplying Decimals 1 decimal place
Course 2
3-3
Multiplying Decimals
To multiply decimals, multiply as you would with integers. To place the decimal point in the product, count the number of decimal places in each factor. The product should have the same number of decimal places in the factors. 7
 8 56
0.7
 0.8
1 decimal place
1 decimal place + 0. 56
2 decimal places
Same digits

17. Additional Example 1: Multiplying Integers by Decimals
Course 2
3-3
Multiplying Decimals
Additional Example 1: Multiplying Integers by Decimals
Multiply.
A. 7 · 0.1 7
 0.1
0.7
B. –3 · 0.03 –3
 0.03
– 0.09

18. Additional Example 1: Multiplying Integers by Decimals
Course 2
3-3
Multiplying Decimals
Additional Example 1: Multiplying Integers by Decimals
Multiply.
C · 35
2.45
 35
12 25
85.75

19. 3-3 Multiplying Decimals Check It Out: Example 1 Multiply. A. 8 · 0.3
Course 2
3-3
Multiplying Decimals
Check It Out: Example 1
Multiply.
A. 8 · 0.3 8
 0.3
2.4
B. –2 · 0.04 –2
 0.04
–0.08

20. 3-3 Multiplying Decimals Check It Out: Example 1 Multiply.
Course 2
3-3
Multiplying Decimals
Check It Out: Example 1
Multiply.
C · 15
3.65
 15
18 25
54.75

21. Additional Example 2A: Multiplying Decimals by Decimals
Course 2
3-3
Multiplying Decimals
Additional Example 2A: Multiplying Decimals by Decimals
Multiply.
2.4 · 1.8
2.4
 1.8
1 92
+ 2 40
4.32
Estimate
2 · 2 = 4

22. Additional Example 2B: Multiplying Decimals by Decimals
Course 2
3-3
Multiplying Decimals
Additional Example 2B: Multiplying Decimals by Decimals
Multiply.
–3.84 · 0.9
–3.84
 0.9
–3.456
Estimate
–4 · 1 = –4

23. 3-3 Multiplying Decimals Check It Out: Example 2A Multiply. 3.2 · 1.6
Course 2
3-3
Multiplying Decimals
Check It Out: Example 2A
Multiply.
3.2 · 1.6
3.2
 1.6
1 92
+ 3 20
5.12
Estimate
3 · 2 = 6

24. 3-3 Multiplying Decimals Check It Out: Example 2B Multiply.
Course 2
3-3
Multiplying Decimals
Check It Out: Example 2B
Multiply.
–2.96 · 0.7
–2.96
 0.7
–2.072
Estimate
–3 · 1 = –3

25. Adding and Subtracting Decimals Insert Lesson Title Here
Course 2
3-2
Adding and Subtracting Decimals
Insert Lesson Title Here
Quiz 1.
2. – (–19.2)
21.25;
–27.66;
Subtract. 3.
6.72 – 4.16
4. 24 – 3.8
2.56;
20.2;

26. Adding and Subtracting Decimals Insert Lesson Title Here
Course 2
3-2
Adding and Subtracting Decimals
Insert Lesson Title Here
Quiz
Subtract.
5. Renee finished her first lap in the 200 m freestyle
event in seconds. She completed the second lap in seconds. By how much did her time increase in the second lap? Estimate to check whether your answer is reasonable.
1.41 seconds;

27. Insert Lesson Title Here
Course 2
3-3
Multiplying Decimals
Insert Lesson Title Here
Lesson Quiz
Multiply.
6. 9 · 0.7
· 1.5
· 4.1
· (–5.4)
10. Dennis runs 7.2 miles per day. How far does he run in 5 days?
6.3
2.4
13.94;
–41.148;
36 miles