Five-Minute Check (over Lesson 2–1)

Main Idea and Vocabulary

Example 1:Use Rounding with Whole Numbers

Example 2:Use Compatible Numbers

Example 3:Use Rounding with Decimals

• I will estimate sums and differences by rounding and using compatible numbers.

• estimate

• compatible numbers

Use Rounding with Whole Numbers

Estimate 923 – 415 by rounding.

Round each number to the nearest hundred. Then subtract.

– 415923

400900

500–

Answer: So, 923 – 415 is about 500.

923 is closer to 900 than 1,000.415 is closer to 400 than 500.

1. A

2. B

3. C

4. D

A B C D

0% 0%0%0%

A. 400

B. 500

C. 550

D. 600

Estimate 812 – 376 by rounding.

Use Compatible Numbers

Gareth’s cat weighs 9.3 pounds. Dieter’s dog weighs 28.9 pounds. Use compatible numbers to estimate the difference.

Find two numbers that you can easily subtract.

– 9.328.9

1030

20–

Answer: So, the difference is about 20 pounds.

28.9 is close to 30.9.3 is close to 10.

1. A

2. B

3. C

4. D

A B C D

0% 0%0%0%

A. 90

B. 80

C. 50

D. 40

Use compatible numbers to estimate the difference 89.3 – 52.2.

Use Rounding with Decimals

Karim wants to buy a baseball mitt that costs $13.95 and a baseball that costs $8.47. Estimate the cost of the two items.

One Way

Round to the nearest ten.

$13.958.47$+ +

$20.00

10.00$10.00$

Another Way

Round to the nearest whole number.

$13.958.47$+ +

$22.00

14.00$8.00$

Use Rounding with Decimals

Answer: Depending on how the numbers are rounded, the difference in cost is about $20.00 or $22.00. The actual cost is $22.42. So, rounding to the nearest whole number gave the more accurate estimate.

1. A

2. B

3. C

4. D0% 0%0%0%

A. $2.00

B. $4.00

C. $8.00

D. $20.00

Estimate the difference in the cost of $12.49 and $7.54.

End of the Lesson

Five-Minute Check (over Lesson 2–1)

Image Bank

Math Tool Chest

Add and Subtract Decimals

1. A

2. B

3. C

4. D

A B C D

0% 0%0%0%

(over Lesson 2–1)

A. 12,340

B. 12,350

C. 12,300

D. 12,400

Round 12,345 to the underlined place.

1. A

2. B

3. C

4. D

A B C D

0% 0%0%0%

(over Lesson 2–1)

A. 593.19

B. 593.000

C. 593.20

D. 593.198

Round 593.197 to the underlined place.

1. A

2. B

3. C

4. D

A B C D

0% 0%0%0%

(over Lesson 2–1)

A. 82.1

B. 83.0

C. 82

D. 82.04

Round 82.03 to the underlined place.

1. A

2. B

3. C

4. D

A B C D

0% 0%0%0%

(over Lesson 2–1)

A. 9.2

B. 10

C. 9.17

D. 9

Round 9.164 to the underlined place.

1. A

2. B

3. C

4. D

A B C D

0% 0%0%0%

(over Lesson 2–1)

A. 816.3

B. 816.31

C. 816.32

D. 816.216

Round 816.295 to the tenths place.

1. A

2. B

3. C

4. D0% 0%0%0%

(over Lesson 2–1)

A. 579.1

B. 580

C. 580.14

D. 580.10

Round 579.139 to the tens place.