Mathematics

Estimation and Rounding

Class 4 | CBSE / NCERT / ICSE

🎯 Learning Objectives

Round numbers to the nearest 10 and the nearest 100.
Estimate sums and differences using rounded numbers.
Use estimation to check if an exact answer is reasonable.
Round 4-digit numbers to the nearest 10 and nearest 100.

📖 Let Us Begin!

Imagine you go to a shop in your town and buy a notebook for Rs 47 and a pen for Rs 23. You want to quickly check if Rs 100 is enough. Instead of adding exactly, you can think: 47 is close to 50 and 23 is close to 20, so the total is about 70. This quick guess is called estimation, and the method we use is called rounding.

Image: Two examples of rounding — the number 47 rounded to nearest 10 becomes 50 (shown on a number line between 40 and 50), and 342 rounded to nearest 100 becomes 300 (shown on a number line between 300 and 400).
Title: Rounding Numbers — Nearest 10 and 100

Rounding to the Nearest 10

Rule: Look at the ones digit. If it is 0, 1, 2, 3, or 4, round down. If it is 5, 6, 7, 8, or 9, round up.

Example

Example 1: Round 63 to the nearest 10.

The ones digit is 3 (less than 5), so round down. 63 rounds to 60.

Example

Example 2: Round 87 to the nearest 10.

The ones digit is 7 (5 or more), so round up. 87 rounds to 90.

Example

Example 3: Round 45 to the nearest 10.

The ones digit is 5 (5 or more), so round up. 45 rounds to 50.

Think: When the ones digit is exactly 5, we always round up. This is the standard rule.

Rounding to the Nearest 100

Rule: Look at the tens digit. If it is 0, 1, 2, 3, or 4, round down. If it is 5, 6, 7, 8, or 9, round up.

Example

Example 4: Round 328 to the nearest 100.

The tens digit is 2 (less than 5), so round down. 328 rounds to 300.

Example

Example 5: Round 672 to the nearest 100.

The tens digit is 7 (5 or more), so round up. 672 rounds to 700.

Rounding 4-Digit Numbers

The same rules apply to larger numbers.

Example

Example 6: Round 3,847 to the nearest 10 and nearest 100.

Nearest 10: ones digit is 7 (round up) -- 3,847 rounds to 3,850.

Nearest 100: tens digit is 4 (round down) -- 3,847 rounds to 3,800.

Example

Example 7: Round 5,263 to the nearest 10 and nearest 100.

Nearest 10: ones digit is 3 (round down) -- 5,263 rounds to 5,260.

Nearest 100: tens digit is 6 (round up) -- 5,263 rounds to 5,300.

Estimating Sums and Differences

To estimate, round each number first, then add or subtract the rounded numbers.

Example

Example 8: Estimate 489 + 213 by rounding to the nearest 100.

489 rounds to 500. 213 rounds to 200. Estimated sum = 500 + 200 = about 700. (Exact answer: 702)

Example

Example 9: Estimate 876 - 342 by rounding to the nearest 100.

876 rounds to 900. 342 rounds to 300. Estimated difference = 900 - 300 = about 600. (Exact answer: 534)

Think: Estimation does not give the exact answer, but it helps you check if your exact answer is reasonable.

📝 Key Words

Word	Meaning
Estimation	Finding an answer that is close to the exact answer, not exact
Rounding	Replacing a number with a nearby number that ends in 0
Round Up	Going to the next higher ten or hundred
Round Down	Going to the lower ten or hundred
Reasonable	An answer that makes sense and is close to the estimate

⭐ Key Points to Remember

To round to the nearest 10, look at the ones digit. 5 or more -- round up. Less than 5 -- round down.
To round to the nearest 100, look at the tens digit. 5 or more -- round up. Less than 5 -- round down.
Estimation helps you quickly check if your exact answer is reasonable.
Round each number first, then add or subtract to get the estimated answer.
The same rounding rules work for 4-digit numbers too.

Finished learning? Now test what you know!

🎯 Quick Quiz — Test Yourself!

Answer these 8 questions about estimation and rounding. Read each one carefully and pick the best answer!

Score: 0 / 8

1. Rounded to the nearest 10, what is 47?

The ones digit is 7 (5 or more), so round up: 47 becomes 50.

2. Rounded to the nearest 10, what is 42?

The ones digit is 2 (less than 5), so round down: 42 becomes 40.

3. When rounding to the nearest 10, which ones digits round UP?

If the ones digit is 5 or more, round up. Less than 5, round down.

4. Rounded to the nearest 100, what is 380?

The tens digit is 8 (5 or more), so round up: 380 becomes 400.

5. Rounded to the nearest 100, what is 230?

The tens digit is 3 (less than 5), so round down: 230 becomes 200.

6. Why is estimation useful?

Estimation helps you quickly check whether your exact answer is reasonable.

7. Round 68 to the nearest 10.

The ones digit is 8, so round up: 68 becomes 70.

8. Estimate 39 + 52 by first rounding each to the nearest 10, then adding.

Round: 39 → 40 and 52 → 50. Then 40 + 50 = 90.

✏️ Practice Questions

A. Round to the Nearest 10

1. 54 rounds to

2. 78 rounds to

3. 135 rounds to

4. 2,461 rounds to

5. 3,095 rounds to

B. Round to the Nearest 100

1. 247 rounds to

2. 562 rounds to

3. 850 rounds to

4. 4,738 rounds to

5. 6,149 rounds to

C. Estimate the Sum or Difference (Round to Nearest 100)

1. 389 + 214: Estimate =

2. 745 + 168: Estimate =

3. 923 - 487: Estimate =

4. 1,560 + 2,340: Estimate =

D. Multiple Choice Questions

1. 67 rounded to the nearest 10 is:

(a) 60(b) 65(c) 70(d) 80

2. Which number rounds to 500 when rounded to the nearest 100?

(a) 430(b) 448(c) 462(d) 539

3. Estimated sum of 291 + 408 (nearest 100) is:

(a) 600(b) 700(c) 800(d) 500

E. Estimate and Check

1. A school ordered 478 notebooks and 325 pencils. Estimate the total by rounding to the nearest 100. Then find the exact total. Is your exact answer close to the estimate?

2. Rohan's father drove 1,876 km in the first week and 2,145 km in the second week. Estimate the total distance by rounding to the nearest 100.

3. A fruit seller had 963 mangoes. He sold 487 mangoes. Estimate how many are left by rounding to the nearest 100. Then find the exact answer.

🎨 Fun Activity -- Estimation at the Market

Imagine you have Rs 500 and you visit a local market. The prices of items are given below. Round each price to the nearest 10 and estimate the total cost. Can you buy all four items?

Item	Actual Price (Rs)	Rounded Price (Rs)
Rice (1 kg)	68
Dal (1 kg)	124
Oil (1 litre)	157
Sugar (1 kg)	43
Estimated Total:

Can you buy all four items with Rs 500?

Want to review the lesson again?

🎯 Learning Objectives

Round numbers to the nearest 10 and the nearest 100.
Estimate sums and differences using rounded numbers.
Use estimation to check if an exact answer is reasonable.
Round 4-digit numbers to the nearest 10 and nearest 100.

📖 Introduction

Imagine buying a notebook for Rs 47 and a pen for Rs 23. Instead of adding exactly, think: 47 ≈ 50 and 23 ≈ 20, so the total is about 70. This quick guess is called estimation, and the method is rounding.

[Image: Rounding Numbers — Nearest 10 and 100. Number 47 on a number line between 40 and 50 rounds to 50. Number 342 on a number line between 300 and 400 rounds to 300.]

Rounding to the Nearest 10

Rule: Look at ones digit. 0–4 → round down. 5–9 → round up.

Ex 1: 63 → ones digit 3 (round down) → 60

Ex 2: 87 → ones digit 7 (round up) → 90

Ex 3: 45 → ones digit 5 (round up) → 50

Rounding to the Nearest 100

Rule: Look at tens digit. 0–4 → round down. 5–9 → round up.

Ex 4: 328 → tens digit 2 (round down) → 300

Ex 5: 672 → tens digit 7 (round up) → 700

Rounding 4-Digit Numbers

Ex 6: 3,847 → nearest 10: 3,850 | nearest 100: 3,800

Ex 7: 5,263 → nearest 10: 5,260 | nearest 100: 5,300

Estimating Sums and Differences

Ex 8: 489 + 213 ≈ 500 + 200 = about 700 (exact: 702)

Ex 9: 876 − 342 ≈ 900 − 300 = about 600 (exact: 534)

Key Words

Word	Meaning
Estimation	Finding an approximate answer
Rounding	Replacing with a nearby number ending in 0
Round Up	Going to the next higher ten/hundred
Round Down	Going to the lower ten/hundred
Reasonable	An answer that makes sense

⭐ Key Points to Remember

Nearest 10: look at ones digit. 5+ → round up. Less than 5 → round down.
Nearest 100: look at tens digit. 5+ → round up. Less than 5 → round down.
Estimation helps you quickly check if your answer is reasonable.
Round each number first, then add or subtract.
Same rules work for 4-digit numbers.

A. Round to the Nearest 10

1. 54 rounds to

2. 78 rounds to

3. 135 rounds to

4. 2,461 rounds to

5. 3,095 rounds to

B. Round to the Nearest 100

1. 247 rounds to

2. 562 rounds to

3. 850 rounds to

4. 4,738 rounds to

5. 6,149 rounds to

C. Estimate the Sum or Difference (Nearest 100)

1. 389 + 214: Estimate =

2. 745 + 168: Estimate =

3. 923 − 487: Estimate =

4. 1,560 + 2,340: Estimate =

D. Multiple Choice Questions

1. 67 rounded to nearest 10 is:

(a) 60(b) 65(c) 70(d) 80

2. Which rounds to 500 (nearest 100)?

(a) 430(b) 448(c) 462(d) 539

3. Estimated sum of 291 + 408 (nearest 100):

(a) 600(b) 700(c) 800(d) 500

E. Estimate and Check

1. A school ordered 478 notebooks and 325 pencils. Estimate total (nearest 100). Then find exact total.

2. Rohan's father drove 1,876 km (week 1) and 2,145 km (week 2). Estimate total distance (nearest 100).

3. A fruit seller had 963 mangoes. He sold 487. Estimate how many left (nearest 100). Find exact answer.

🎨 Activity — Estimation at the Market

You have Rs 500. Round each price to nearest 10 and estimate the total.

Item	Actual (Rs)	Rounded (Rs)
Rice (1 kg)	68
Dal (1 kg)	124
Oil (1 litre)	157
Sugar (1 kg)	43
Estimated Total:

Can you buy all four items with Rs 500?

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Estimation and Rounding

🎯 Learning Objectives

📖 Let Us Begin!

Rounding to the Nearest 10

Rounding to the Nearest 100

Rounding 4-Digit Numbers

Estimating Sums and Differences

📝 Key Words

🎯 Quick Quiz — Test Yourself!

✏️ Practice Questions

Estimation and Rounding

Estimation and Rounding (continued)