Mrs. Lefeld's Leaping Learners



Round to the Nearest Whole Number Math Talk Notes

4 5

4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0

1. Plot a point at 4.7 and follow the steps below to discuss how a number line can be used to round 4.7 to the nearest whole number.

2. On this number line, 4.7 is between which two whole numbers? 4 and 5

3. This means when we round 4.7 to the nearest whole number, the answer will be … either 4 or 5.

4. What number is exactly halfway between 4 and 5? 4.5

5. Is 4.7 to the right or left of 4.5? to the right, which means it is more than halfway between the two whole numbers

6. Is 4.7 closer to 4 or closer to 5? closer to 5

7. So, what is 4.7 rounded to the nearest whole number? 5

8. Why is 4 not the correct answer? Since 4.5 is exactly halfway between 4 and 5 and 4.7 is to the right of 4.5, 4.7 is closer to 5 than to 4. Therefore, 4.7 rounds to 5.

9. Repeat steps 2 – 8 for 4.4. 4.4 rounds to 4

Round to the Nearest Tenth Math Talk Notes

1.6 1.7

1.60 1.61 1.62 1.63 1.64 1.65 1.66 1.67 1.68 1.69 1.70

1. Plot a point at 1.62 and follow the steps below to discuss how a number line can be used to round 1.62 to the nearest whole number.

2. On this number line, 1.62 is between which two numbers? 1.6 and 1.7

3. This means when we round 1.62 to the nearest tenth, the answer will be … either 1.6 or 1.7.

4. What number is exactly halfway between 1.6 and 1.7? 1.65

5. How do you know this number is halfway between? Besides being able to see that on the number line, students should mention that 1.6 is the same as 1.60 and 1.7 is the same as 1.70. Halfway between 0.60 and 0.70 is 0.65; therefore halfway between 1.60 and 1.70 is 1.65 so 1.65 is halfway between 1.6 and 1.7.

6. Is 1.62 to the right or left of 1.65? to the left, which means it is less than halfway between 1.6 and 1.7

7. Is 1.62 closer to 1.6 or closer to 1.7? closer to 1.6

8. So, what is 1.62 rounded to the nearest tenth? 1.6

9. Why is the answer 1.6 and not 1.60? Since we are asked to round to the nearest tenth, the answer should end in the tenths place, not the hundredths place.

10. Why is 1.7 not the correct answer? Since 1.65 is exactly halfway between 1.6 and 1.7 and 1.62 is to the left of 1.65, 1.62 is closer to 1.6 than to 1.7. Therefore, 1.62 rounds to 1.6.

11. Repeat steps 2 – 8 for 1.68. 1.68 rounds to1.7

Round to the Nearest Hundredth Math Talk Notes

8 9

8.0 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 9.0

1. Discuss what whole numbers 8.257 is between. (8 and 9) Set up the number line as pictured above.

2. Plot a point where 8.257 would fall on this number line. (Between 8.2 and 8.3, slightly past the halfway point between 8.2 and 8.3)

3. Create a new number line by hundredths and plot a point where 8.257 would fall. (Between 8.25 and 8.26, closer to 8.26)

8.2 8.3

8.20 8.21 8.22 8.23 8.24 8.25 8.26 8.27 8.28 8.29 8.30

4. Create a new number line by thousandths and plot a point at 8.257. Then, follow the steps below to discuss how a number line can be used to round 8.257 to the nearest hundredth.

8.25 8.26

8.250 8.251 8.252 8.253 8.254 8.255 8.256 8.257 8.258 8.259 8.260

5. On this number line, 8.257 is between which two numbers? (8.25 and 8.26)

6. This means when we round 8.257 to the nearest hundredth, the answer will be … either 8.25 and 2.26.

7. What number is exactly halfway between 8.25 and 8.26? (8.255) How do you know this number is halfway between? (Besides being able to see that on the number line, students should mention that 8.25 is the same as 8.250 and 8.26 is the same as 8.260. Halfway between 0.250 and 0.260 is 0.255; therefore halfway between 8.250 and 8.260 is 8.255 so 8.255 is halfway between 8.25 and 8.26.)

8. Is 8.257 to the right or left of 8.255? (to the right, which means it is more than halfway between 8.25 and 8.26)

9. Is 8.257 closer to 8.25 or closer to 8.26? (closer to 8.26) So, what is 8.257 rounded to the nearest hundredth? (8.26)

10. Why is the answer 8.26 and not 8.260? (Since we are asked to round to the nearest hundredth, the answer should end in the hundredths place, not the thousandths place.)

11. Why is 8.25 not the correct answer? (Since 8.255 is exactly halfway between 8.25 and 8.26 and 8.257 is to the left of 8.255, 8.257 is closer to 8.26 than to 8.25. Therefore, 8.257 rounds to 8.26.)

12. Repeat steps 2 – 8 for 8.253. (8.253 rounds to 8.25)

Practice Rounding Decimals Using Number Lines p. 1

Directions: Use the number lines provided to show how to round each decimal to the given place value. Space has been provided in case you need to create more than one number line to help “zoom in” when dealing with rounding to the nearest hundredth.

1. Round 7.6 to the nearest whole number.

2. Round 8.55 to the nearest tenth.

3. Round 51.212 to the nearest hundredth.

Practice Rounding Decimals Using Number Lines p.2

4. Round 31.45 to the nearest whole number.

5. Round 0.84 to the nearest tenth.

6. Round 0.898 to the nearest hundredth

Practice Rounding Decimals

Using Number Lines p. 1 & p. 2 – Answer Key

1. 7.6 rounded to the nearest whole number is 8

2. 8.55 rounded to the nearest tenth is 8.6

3. 51.212 rounded to the nearest hundredth is 51.21

4. 31.45 rounded to the nearest whole number is 31

5. 0.84 rounded to the nearest tenth is 0.8

6. 0.898 rounded to the nearest hundredth is 0.90

Name: ________________________

Date: ________________________

Use Number Lines to Round Numbers

Journal Prompt

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Mathematics Alignment Lesson

Grade 5 Quarter 1 Day 24

Alignment Lesson

Round Decimals Using Number Lines

1. Draw a number line by tenths from 4.0 to 5.0 on the board. Use the guiding questions on “Round to the Nearest Whole Number Math Talk Notes” to discuss how the number line can be used to round 4.7 to the nearest whole number; and then repeat for 4.4.

2. Have students repeat the same process by creating a number line on their MathBoard to round 8.3 to the nearest whole number.

3. Draw a number line on the board and, to begin, only label 1.6 and 1.7 above the number line and ask students what each line on the number line must represent (one hundredth) and how they know (ten hundredths make up one tenth). Use the guiding questions on “Round to the Nearest Tenth Math Talk Notes” to discuss how the number line can be used to round 1.62 to the nearest tenth; and then repeat for 1.68.

4. Have students repeat the same process by creating a number line on the MathBoard to round 51.16 to the nearest tenth.

5. To model how to use a number line to round a number to the nearest hundredth, begin by drawing a number line by tenths from 8 to 9. Use the guiding questions on “Round to the Nearest Hundredth Math Talk Notes” to discuss how to use several number lines to round to the nearest hundredth. Liken this to “zooming in” on the number line to help students see why it is helpful to go through these steps. Once they have a good understanding of this, they can build a number by thousandths to round instead.

6. Have students repeat the same process by creating a number line on the MathBoard to round 16.686 to the nearest hundredth.

7. Students begin to work on Transparency/Blackline Master, “Practice Rounding Decimals Using Number Lines p. 1 and p. 2”. This may be completed for homework along with the “Use Number Lines to Round Decimals Journal Prompt”.

Note: Some students may benefit from highlighting the numbers to the left and right of the halfway mark to help round. They should color the numbers to the left of the halfway point one color and the numbers to the right of the halfway point another color.

Common Core State Standard(s)

|5.NBT.4 Use place value understanding to |

|round decimals to any place. |

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Standards for Mathematical Practice

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|Standard 4 Model with mathematics. |

|Standard 7 Look for and make use of |

|structure. |

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Materials Needed:

• Transparency/Blackline Master-“Practice Rounding Decimals Using Number Lines”

• Blackline Master – “Use Number Lines to Round Decimals Journal Prompt”

• MathBoards

• Whiteboard markers

Assessment

Informal - “Use Number Lines to Round Decimals Journal Prompt”

WCPSS/PROJECT ACHIEVE/C&I/2001

LEARNING STRATEGIES:

Homework

Blackline Master, “Practice Rounding Decimals Using Number Lines”

Vocabulary

None Referenced.

Source: Teacher Created, Math Expressions U3, L15

Write a letter to a friend to explain how to use a number line to help round decimal numbers. Use one of the problems from Practice Rounding Decimals Using Number Lines p. 1 or p.2 to support your letter. Be sure to sure precise math vocabulary.

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