Rounding Numbers

Why Round Numbers?

Rounding makes numbers easier to work with by making them simpler.

Real-life examples:

• "About 30 students in class" instead of "27 students"
• "Around $50" instead of "$47.82"
• "Nearly 100 people" instead of "96 people"

Rounding Rules

The basic rule:

• If the digit you're looking at is 5 or more, round UP
• If the digit is 4 or less, round DOWN

Remember: "Five or more? Raise the score! Four or less? Let it rest!"

Rounding to the Nearest 10

When rounding to the nearest 10, you're rounding the tens digit (or adding a new tens digit).

Steps:

1. Find the tens place (the digit you're rounding)
2. Look at the digit to the right (the ones place)
3. If it's 5 or more → round the tens digit up
4. If it's 4 or less → keep the tens digit the same
5. Replace the ones digit with 0

Examples:

• 27 → Rounding the 2 in the tens place → Look at 7 (ones) → 7 ≥ 5 → Round up to 30
• 43 → Rounding the 4 in the tens place → Look at 3 (ones) → 3 < 5 → Keep as 40
• 85 → Rounding the 8 in the tens place → Look at 5 (ones) → 5 = 5 → Round up to 90
• 92 → Rounding the 9 in the tens place → Look at 2 (ones) → 2 < 5 → Keep as 90

Rounding to the Nearest 100

When rounding to the nearest 100, you're rounding the hundreds digit (or adding a new hundreds digit).

Steps:

1. Find the hundreds place (the digit you're rounding)
2. Look at the digit to the right (the tens place)
3. If it's 5 or more → round the hundreds digit up
4. If it's 4 or less → keep the hundreds digit the same
5. Replace tens and ones with 0

Examples:

• 347 → Rounding the 3 in the hundreds place → Look at 4 (tens) → 4 < 5 → Keep as 300
• 682 → Rounding the 6 in the hundreds place → Look at 8 (tens) → 8 ≥ 5 → Round up to 700
• 450 → Rounding the 4 in the hundreds place → Look at 5 (tens) → 5 = 5 → Round up to 500
• 199 → Rounding the 1 in the hundreds place → Look at 9 (tens) → 9 ≥ 5 → Round up to 200

Rounding to the Nearest 1,000

When rounding to the nearest 1,000, you're rounding the thousands digit (or adding a new thousands digit).

Steps:

1. Find the thousands place (the digit you're rounding)
2. Look at the digit to the right (the hundreds place)
3. Apply the rounding rule to the thousands digit
4. Replace hundreds, tens, and ones with 0

Examples:

• 3,621 → Rounding the 3 in the thousands place → Look at 6 (hundreds) → 6 ≥ 5 → Round up to 4,000
• 7,389 → Rounding the 7 in the thousands place → Look at 3 (hundreds) → 3 < 5 → Keep as 7,000
• 5,500 → Rounding the 5 in the thousands place → Look at 5 (hundreds) → 5 = 5 → Round up to 6,000

Using a Number Line

A number line helps you see which number is closer:

For 27:

20 ←―――27―――→ 30

27 is closer to 30, so round to 30 ✓

For 43:

40 ←―43――――→ 50

43 is closer to 40, so round to 40 ✓

Practice Strategy

Quick method:

1. Underline the place you're rounding to
2. Circle the digit to the right
3. Use the rule: 5+ up, 4- down
4. Change all digits to the right to zeros

Example: Round 3,678 to nearest hundred

• Underline: 3,678 (rounding the 6 in hundreds place)
• Circle: 3,678 (looking at the 7 in tens place)
• 7 ≥ 5, so round the hundreds digit up: 6 → 7
• Answer: 3,700

Common Mistakes

❌ Looking at the wrong digit ❌ Forgetting to change digits to the right to zero ❌ Rounding 5 down instead of up

✅ Always look ONE place to the right of where you're rounding ✅ Remember: 5 rounds UP ✅ Replace all digits to the right with zeros