Rounding Number Landmarks

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Date:

Part 1: Find the landmarks

WALT: We are learning to round numbers to the nearest 10 and 100 using number landmarks and number lines.

Success criteria: I can find the nearest landmarks. I can explain which landmark a number is closest to. I can round to the nearest 10 or 100.

Remember: Find the two multiples on either side. A number halfway between two landmarks rounds up.

Worked example

Round 43 to the nearest 10. The landmarks are 40 and 50. Since 43 is closer to 40, 43 rounds to 40.

40 ───── 43 ───────── 50

1. Write the two nearest landmarks for each number.

a) 24 is between ______ and ______.

b) 58 is between ______ and ______.

c) 238 is between ______ and ______ when rounding to the nearest 100.

d) 671 is between ______ and ______ when rounding to the nearest 100.

2. Use the number line. Round 46 to the nearest 10. Circle the closer landmark and write the answer.

40 ───── 45 ───── 46 ───────── 50

46 rounds to ______.

3. Use the landmarks. Round 326 to the nearest 100. Explain why.

300 ───────── 350 ───────── 400

Part 2: Round the numbers

Find the landmarks first. Then decide whether to round up or down.

4. Round each number to the nearest 10.

24 → ______ 58 → ______ 71 → ______ 145 → ______

5. Round each number to the nearest 100.

238 → ______ 671 → ______

6. Complete the mixed set.

a) 37 to the nearest 10: ______

b) 84 to the nearest 10: ______

c) 149 to the nearest 100: ______

d) 850 to the nearest 100: ______

7. Show your thinking for one answer from Questions 4–6. Use a number line, landmarks, or words.

8. Extension: 450 is halfway between 400 and 500. Which way does it round to the nearest 100? Explain.

Part 3: Estimate and check

Use rounding when an exact answer is not needed. You may answer orally if that helps you show your thinking.

9. A rural school has 47 people at a sports day. About how many people is that to the nearest 10? Explain your estimate.

10. A farm shop packs 326 apples. About how many apples is that to the nearest 100?

About ______ apples. The number is closer to ______ than ______.

Exit ticket

a) 67 rounded to the nearest 10 is ______.

b) 349 rounded to the nearest 100 is ______.

c) I know because ________________________________________________.

Support options

Use a large number line, counters, or place-value blocks. Start with numbers up to 120. Read one question at a time. Use the sentence starter: “_____ is between _____ and _____. It is closer to _____ because _____.”

Teacher answer key

1. a) 20 and 30 b) 50 and 60 c) 200 and 300 d) 600 and 700

2. 50

3. 300; 326 is 26 away from 300 and 74 away from 400.

4. 20, 60, 70, 150

5. 200, 700

6. a) 40 b) 80 c) 100 d) 900

7. Answers should show correct landmarks and a clear rounding decision.

8. 500; halfway cases round up.

9. About 50 people; 47 is closer to 50 than 40.

10. About 300 apples; 326 is closer to 300 than 400.

Exit ticket: a) 70 b) 300 c) Accept an explanation using landmarks, distance, or a number line.

Curriculum connection: NZ Te Mātaiaho Mathematics and Statistics, Number / Number structures: NZ-TMA-MATHEMATIC-Y0-10-number-011-DOC139 and NZ-TMA-MATHEMATIC-Y0-10-number-009-DOC139.