Round Whole Numbers to Nearest 10 or 100: Complete Guide for Grade 3

Learn how to round whole numbers to the nearest 10 or 100 with visual number lines, step-by-step instructions, and practice problems for 3rd grade students.

Rounding to the Nearest 10
1 Understanding Rounding to 10
Concept:

Rounding to nearest 10: Finding the closest multiple of 10 to a given number

40
41
42
43
44
45
46
47
50
↑
45
Rule for rounding to 10:

• Look at the ones digit

• If ones digit is 0-4, round down

• If ones digit is 5-9, round up

Step 1: Identify the tens and ones digits

For 47: tens = 4, ones = 7

Step 2: Look at the ones digit

Ones digit is 7

Step 3: Apply the rule

7 is greater than 5, so round up

Step 4: Round to nearest 10

47 rounds up to 50

47 rounded to nearest 10 is 50
2 Rounding Examples to 10
Example 1: 32

Ones digit = 2 (less than 5)

Round down to 30

Example 2: 58

Ones digit = 8 (greater than 5)

Round up to 60

Example 3: 65

Ones digit = 5 (equals 5)

Round up to 70

Example 4: 94

Ones digit = 4 (less than 5)

Round down to 90

Memory Aid: "5 or more, raise the score; 4 or less, let it rest"
1
Look at the ones digit
2
Decide: 0-4 round down, 5-9 round up
3
Change ones digit to 0
3 Rounding to Nearest 100
Concept:

Rounding to nearest 100: Finding the closest multiple of 100 to a given number

300
325
350
375
400
↑
378
Rule for rounding to 100:

• Look at the tens digit (and ones digit)

• If last two digits are 00-49, round down

• If last two digits are 50-99, round up

Step 1: Identify the hundreds, tens, and ones digits

For 378: hundreds = 3, tens = 7, ones = 8

Step 2: Look at the last two digits

Last two digits are 78

Step 3: Apply the rule

78 is greater than 50, so round up

Step 4: Round to nearest 100

378 rounds up to 400

378 rounded to nearest 100 is 400
Trick: Only look at the tens digit when rounding to 100. If tens digit is 5 or more, round up. If tens digit is 4 or less, round down.
Complete Summary: Rounding Whole Numbers
Round to 10: Look at Ones Digit
Rounding Rule
Key Definitions:

Rounding: Changing a number to the nearest 10, 100, or other place value

Nearest 10: The closest multiple of 10 to a given number

Nearest 100: The closest multiple of 100 to a given number

Estimation: Using rounded numbers to get an approximate answer

Place value: The value of a digit based on its position in a number

Rounding Method:
  1. Identify the target place: Determine whether rounding to 10 or 100
  2. Find the relevant digit: Look at the ones digit (for 10s) or tens digit (for 100s)
  3. Apply the rule: 0-4 round down, 5-9 round up
  4. Change accordingly: Set lower digits to zero
  5. Verify: Check that the rounded number makes sense
Round to 10
Ones digit
0-4→down, 5-9→up
Round to 100
Tens digit
0-4→down, 5-9→up
Estimation
Approximation
Quick mental math
Tip 1: Use number lines to visualize the rounding process.
Tip 2: Remember: 5 is the halfway point that always rounds up.
Tip 3: Practice with multiples of 10 and 100 first.
Tip 4: Check your work by ensuring the rounded number is reasonable.
Common applications: Estimating sums, checking answers, real-world approximations.
Mathematical foundation: Builds number sense and place value understanding.
Essential Rounding Rules:

• Digit rule: Look at the digit to the right of the target place

• 5 rule: When the digit is exactly 5, always round up

• Zero rule: Lower digits become zeros after rounding

• Direction rule: Round up or down based on proximity to multiples

Practice Problems & Solutions
4 Rounding Practice
Round to Nearest 10:

Problem 1: 47

Solution: Ones digit is 7 → 5 or more → Round up to 50

Problem 2: 82

Solution: Ones digit is 2 → 4 or less → Round down to 80

Problem 3: 95

Solution: Ones digit is 5 → Round up to 100

Problem 4: 31

Solution: Ones digit is 1 → 4 or less → Round down to 30

Round to Nearest 100:

Problem 5: 347

Solution: Tens digit is 4 → 4 or less → Round down to 300

Problem 6: 568

Solution: Tens digit is 6 → 5 or more → Round up to 600

Problem 7: 750

Solution: Tens digit is 5 → Round up to 800

Problem 8: 231

Solution: Tens digit is 3 → 4 or less → Round down to 200

Self-Check:

• Did I identify the correct digit to look at?

• Did I apply the correct rounding rule?

• Does my answer make sense in the context?

5 Word Problems
Problem 1: Sarah collected 87 seashells. About how many seashells did she collect when rounded to the nearest 10?

Solution: 87 has ones digit 7. Since 7 ≥ 5, round up to 90.

Answer: About 90 seashells

Problem 2: A school has 423 students. About how many students when rounded to the nearest 100?

Solution: 423 has tens digit 2. Since 2 ≤ 4, round down to 400.

Answer: About 400 students

Word Problem Strategy:

• Identify the number: Find the specific number mentioned

• Identify the rounding target: Determine if rounding to 10 or 100

• Apply the rule: Use the appropriate rounding method

• State the answer: Include "about" or "approximately"

Estimation & Problem Solving
Estimate = Round Then Calculate!
Estimation Strategy
Estimation Concept:

Estimation: Using rounded numbers to quickly find an approximate answer

Example: 47 + 32
Round first: 50 + 30
Estimate: 80
Actual: 79
Estimation Benefits: Quick mental math, checking reasonableness, making decisions faster
Tip 1: Use estimation to check if your exact answer is reasonable.
Tip 2: Practice estimation regularly to improve number sense.
Tip 3: Estimate before calculating to predict the answer range.
Success indicators: Accurate rounding, reasonable estimates, improved mental math.
Real-world connection: Estimation is used in shopping, budgeting, and planning.
Estimation Mastery:

• ✓ I can round numbers to the nearest 10 or 100

• ✓ I can use rounding to estimate sums and differences

• ✓ I can verify if my exact answer is reasonable

• ✓ I understand when estimation is appropriate

• ✓ I can explain my estimation strategy

Rounding Process

📊
Identify Target

Round to 10 or 100

Find Digit

Look at ones or tens digit

Apply Rule

0-4 round down, 5-9 round up

Verify

Check if answer makes sense

Questions & Answers

Question: I don't understand why 45 rounds up to 50 instead of down to 40. Isn't 45 closer to 40?

Answer: Actually, 45 is exactly in the middle between 40 and 50! It's the same distance from both numbers:

  • Distance from 45 to 40 = 5
  • Distance from 45 to 50 = 5

Mathematical convention: When a number is exactly in the middle, we always round up to avoid bias in calculations.

Think of it like a tie-breaker in sports - when there's a tie, there needs to be a rule for who wins. The mathematical rule is to round up when there's a tie (when the digit is 5).

So: 41, 42, 43, 44 round down to 40, but 45, 46, 47, 48, 49 round up to 50.

This keeps the rounding system consistent and fair!

Question: How can I help my child practice rounding at home in a fun way?

Answer: Here are fun home practice ideas:

  • Grocery store math: Round prices to nearest 10¢ or $1 when shopping
  • Age rounding: Round ages of family members to nearest 10
  • Time estimation: Round minutes to nearest 10 (37 minutes ≈ 40 minutes)
  • Household items: Count and round collections (toys, books, etc.)
  • Number line walks: Draw a number line on paper and have them jump to rounded numbers

Create a "Rounding Game": Roll two dice to make a 2-digit number, then round it to the nearest 10.

Use real objects like blocks or coins to build numbers and then round them.

Make it competitive: Who can round numbers the fastest? Who gets the most correct?

Question: What's the difference between rounding to 10 and rounding to 100? How do I know which one to do?

Answer: Here's how to tell the difference:

  • Rounding to 10: Look at the ones digit (the last digit)
  • Rounding to 100: Look at the tens digit (second from last)

For rounding to 10:

  • Example: 73 → Look at 3 (ones digit) → Round down to 70
  • Example: 76 → Look at 6 (ones digit) → Round up to 80

For rounding to 100:

  • Example: 347 → Look at 4 (tens digit) → Round down to 300
  • Example: 367 → Look at 6 (tens digit) → Round up to 400

The problem will tell you which to do: "round to nearest 10" or "round to nearest 100".

Remember: The target place value tells you which digit to look at!