do now estimate by rounding to the nearest integer. 1. 3.62 + 4.1 2. 7.47 + (–8.23) 3. 8.52 –...

Do NowEstimate by rounding to the nearest integer.

1. 3.62 + 4.1

2. 7.47 + (–8.23)

3. 8.52 – 3.16

4. 5.826 + 11.729

8

–1

6

Course 2

3-2 Adding and Subtracting Decimals

18

Hwk: p 25, 26

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

Course 2

3-2 Adding and Subtracting Decimals

EQ: How do I add/subtract/multiply/divide decimals?

Course 2

3-2 Adding and Subtracting Decimals

M7N1.c Add, subtract, multiply, and divide positive and negative rational numbers

Course 2

3-2 Adding and Subtracting Decimals

Use zero as a placeholder so thatboth numbers have the same numberof digits after their decimal points.

Add each column just as you wouldadd integers.

Line up the decimal points.

70.8

66.8+ 4.0

Add 66.8 and 4

Course 2

3-2 Adding and Subtracting Decimals

4.55 + 11.3

4.55+ 11.30

15.85

Estimate5 + 11 = 16

Course 2

3-2 Adding and Subtracting Decimals

6.44 + 16

6.44+ 16.00

22.44

Estimate6 + 16 = 22

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!

Course 2

3-2 Adding and Subtracting Decimals

Course 2

3-2 Adding and Subtracting Decimals–8.33 + (–10.972)

Estimate

–8 + (–11) = –19

Course 2

3-2 Adding and Subtracting Decimals6.78 + 13.2

19.98

Estimate7 + 13 = 20

Course 2

3-2 Adding and Subtracting Decimals

4.21 + 34

38.21

Estimate4 + 34 = 38

Course 2

3-2 Adding and Subtracting Decimals–7.89 + (–13.852)

= –21.742

Estimate

–8 + (–14) = –22

Course 2

3-2 Adding and Subtracting Decimals

A. 5.34 – 2.08

3.26

B. 28 – 15.911

28.000 –15.911

12.089

7 9 9 10

Course 2

3-2 Adding and Subtracting Decimals

A. 3.57 – 1.46

2.11

B. 34 – 12.462

34.000 –12.462

21.538

3 9 9 10

Course 2

3-2 Adding and Subtracting DecimalsDuring one month in the United States, 492.23million commuter trips were taken on buses, and 26.331 million commuter trips were takenon light rail. What was the total number of tripstaken on buses and light rail?

492.230+26.331

The total number of trips was 518.561 million.

Insert Lesson Title Here

Course 2

3-2 Adding and Subtracting Decimals

143.660

+169.831

The total number of bushels was 313.491 million.

In 1999, 143.66 million bushels of corn were grown in the United States. In 2000, the harvestyielded 169.831 million bushels. What was the total production for those two years?

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.

7 856 56

0.7 0.8

1 decimal place

1 decimal place

2 decimal places

+

Same digits

0.

Multiply.

Additional Example 1: Multiplying Integers by Decimals

Course 2

3-3 Multiplying Decimals

A. 7 · 0.1

7 0.1

0.7

B. –3 · 0.03

–3 0.03– 0.09

Multiply.

Additional Example 1: Multiplying Integers by Decimals

Course 2

3-3 Multiplying Decimals

C. 2.45 · 35

2.45 35

12 25+ 73 50

85.75

Multiply.

Check It Out: Example 1

Course 2

3-3 Multiplying Decimals

A. 8 · 0.3

8 0.3

2.4

B. –2 · 0.04

–2 0.04–0.08

Multiply.

Check It Out: Example 1

Course 2

3-3 Multiplying Decimals

C. 3.65 · 15

3.65 15

18 25+ 36 50

54.75

Multiply.

Additional Example 2A: Multiplying Decimals by Decimals

Course 2

3-3 Multiplying Decimals

2.4 · 1.8

2.4 1.8

1 92 + 2 40

4.32

Estimate2 · 2 = 4

Multiply.

Additional Example 2B: Multiplying Decimals by Decimals

Course 2

3-3 Multiplying Decimals

–3.84 · 0.9

–3.84 0.9

–3.456

Estimate–4 · 1 = –4

Multiply.

Check It Out: Example 2A

Course 2

3-3 Multiplying Decimals

3.2 · 1.6

3.2 1.6

1 92 + 3 20

5.12

Estimate3 · 2 = 6

Multiply.

Check It Out: Example 2B

Course 2

3-3 Multiplying Decimals

–2.96 · 0.7

–2.96 0.7

–2.072

Estimate–3 · 1 = –3

Quiz

Insert Lesson Title Here

2.56;

Course 2

3-2 Adding and Subtracting Decimals

21.25; –27.66;

4. 24 – 3.8

20.2;

1. 6.98 + 14.27 2. –8.46 + (–19.2)

3. 6.72 – 4.16

Subtract.

Quiz

Insert Lesson Title Here

Course 2

3-2 Adding and Subtracting Decimals

Subtract.

5. Renee finished her first lap in the 200 m freestyleevent in 28.76 seconds. She completed the second lap in 30.17 seconds. By how much did her time increase in the second lap? Estimate to check whether your answer is reasonable.

1.41 seconds;

Lesson Quiz

Multiply.

6. 9 · 0.7

7. 1.6 · 1.5

8. 3.4 · 4.1

9. 7.62 · (–5.4)

10. Dennis runs 7.2 miles per day. How far does he run in 5 days?

2.4

6.3

Insert Lesson Title Here

13.94;

–41.148;

Course 2

3-3 Multiplying Decimals

36 miles