Rounding to Nearest 10 and 100
Rounding means replacing a number with a nearby number that is easier to work with. We can round numbers to the nearest 10 or the nearest 100.
Rounding is useful for estimating answers quickly. For example, if a book costs ₹78, we can round it to ₹80 for quick mental math.
What is Rounding to Nearest 10 and 100 - Class 3 Maths (Numbers up to 1000)?
Rounding to the nearest 10: Look at the ones digit.
- If the ones digit is 0, 1, 2, 3, or 4 → round down (keep the tens digit).
- If the ones digit is 5, 6, 7, 8, or 9 → round up (add 1 to the tens digit).
Rounding to the nearest 100: Look at the tens digit.
- If the tens digit is 0, 1, 2, 3, or 4 → round down (keep the hundreds digit).
- If the tens digit is 5, 6, 7, 8, or 9 → round up (add 1 to the hundreds digit).
Rule: 5 or more → round up. Less than 5 → round down.
Solved Examples
Example 1: Rounding to Nearest 10 — Round Down
Question: Round 432 to the nearest 10.
Think:
- Ones digit = 2
- 2 < 5, so round down
- 432 → 430
Answer: 432 rounded to the nearest 10 is 430.
Example 2: Rounding to Nearest 10 — Round Up
Question: Round 567 to the nearest 10.
Think:
- Ones digit = 7
- 7 ≥ 5, so round up
- 567 → 570
Answer: 567 rounded to the nearest 10 is 570.
Example 3: Rounding to Nearest 10 — Ones Digit is 5
Question: Round 345 to the nearest 10.
Think:
- Ones digit = 5
- 5 = 5, so round up
- 345 → 350
Answer: 345 rounded to the nearest 10 is 350.
Example 4: Rounding to Nearest 100 — Round Down
Question: Round 623 to the nearest 100.
Think:
- Tens digit = 2
- 2 < 5, so round down
- 623 → 600
Answer: 623 rounded to the nearest 100 is 600.
Example 5: Rounding to Nearest 100 — Round Up
Question: Round 478 to the nearest 100.
Think:
- Tens digit = 7
- 7 ≥ 5, so round up
- 478 → 500
Answer: 478 rounded to the nearest 100 is 500.
Example 6: Rounding to Nearest 100 — Tens Digit is 5
Question: Round 750 to the nearest 100.
Think:
- Tens digit = 5
- 5 = 5, so round up
- 750 → 800
Answer: 750 rounded to the nearest 100 is 800.
Example 7: Word Problem — Estimating Cost
Question: Ria buys a bag for ₹387. Round the price to the nearest ₹10 and the nearest ₹100.
Think:
- Nearest 10: ones digit = 7 ≥ 5, round up → ₹390
- Nearest 100: tens digit = 8 ≥ 5, round up → ₹400
Answer: Nearest 10 = ₹390. Nearest 100 = ₹400.
Example 8: Rounding Near 1000
Question: Round 958 to the nearest 100.
Think:
- Tens digit = 5
- 5 = 5, so round up
- 958 → 1000
Answer: 958 rounded to the nearest 100 is 1000.
Example 9: Word Problem — School Attendance
Question: 843 students attended sports day. Round this to the nearest 10 and nearest 100.
Think:
- Nearest 10: ones = 3 < 5, round down → 840
- Nearest 100: tens = 4 < 5, round down → 800
Answer: Nearest 10 = 840. Nearest 100 = 800.
Example 10: Already a Multiple of 10
Question: Round 460 to the nearest 10.
Think:
- Ones digit = 0
- 460 is already a multiple of 10
Answer: 460 rounded to the nearest 10 is 460 (no change).
Real-World Applications
Where is rounding used in daily life?
- Shopping: 'This toy costs about ₹500' (actual price ₹489). Shopkeepers and customers both round prices for quick estimates.
- Population: 'Our school has about 800 students' (actual: 783). Official reports often use rounded numbers.
- Cooking: 'Add about 250 g of flour' instead of exactly 247 g.
- Distance: 'Delhi to Agra is about 200 km' (actual: 233 km).
- Time: 'The movie is about 2 hours long' (actual: 1 hour 54 minutes).
- News: Newspapers report rounded figures: 'About 500 people attended the event.'
Rounding makes numbers easier to understand and communicate. It is used whenever an approximate answer is good enough and exact precision is not needed.
Key Points to Remember
- Rounding makes numbers easier to work with for estimation.
- Nearest 10: Look at the ones digit. 5 or more → round up; less than 5 → round down.
- Nearest 100: Look at the tens digit. 5 or more → round up; less than 5 → round down.
- If a number is already a multiple of 10 or 100, it stays the same when rounded.
- Rounding to nearest 100 can give 1000 (e.g., 960 → 1000).
- Rounding is used for estimation, not for exact answers.
Practice Problems
- Round 276 to the nearest 10.
- Round 534 to the nearest 100.
- Round 895 to the nearest 10 and nearest 100.
- Aman has ₹462. Round his money to the nearest ₹100.
- Which numbers between 40 and 50 round to 50 when rounded to the nearest 10?
- Round 505 to the nearest 10 and nearest 100.
- A school has 748 students. About how many is that, rounded to the nearest 100?
Frequently Asked Questions
Q1. What does rounding a number mean?
Rounding means replacing a number with a nearby number that is simpler. For example, 78 rounded to the nearest 10 is 80.
Q2. What is the rule for rounding?
Look at the digit to the right of the place you are rounding to. If it is 5 or more, round up. If it is less than 5, round down.
Q3. What happens when the digit is exactly 5?
When the digit is exactly 5, we round up. For example, 35 rounds to 40 (nearest 10), and 250 rounds to 300 (nearest 100).
Q4. Can rounding give a wrong answer?
Rounding gives an approximate answer, not an exact one. It is used for estimation. For exact calculations, use the original numbers.
Q5. Why is rounding useful?
Rounding helps with quick mental math. If you need to estimate the total cost of items priced at ₹48 and ₹73, round them to ₹50 and ₹70 for an easy estimate of ₹120.
Q6. What is the difference between rounding to nearest 10 and nearest 100?
When rounding to nearest 10, look at the ones digit. When rounding to nearest 100, look at the tens digit. Nearest 100 gives a rougher approximation than nearest 10.
Q7. Can a 3-digit number round to 1000?
Yes. Numbers from 950 to 999 round to 1000 when rounded to the nearest 100.
Q8. Does 0 in the ones place mean the number is already rounded?
A number ending in 0 (like 340) is already a multiple of 10, so rounding to the nearest 10 gives the same number. But it may not be a multiple of 100, so rounding to the nearest 100 may change it (340 → 300).
