Mathematics -- Class 4

Topic: Estimation and Rounding
Name: ____________________________Class: 4Date: ________________
Learning Objectives
A Friendly Introduction

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.

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 1: Round 63 to the nearest 10.

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

Example 2: Round 87 to the nearest 10.

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

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 4: Round 328 to the nearest 100.

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

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 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 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 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 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
WordMeaning
EstimationFinding an answer that is close to the exact answer, not exact
RoundingReplacing a number with a nearby number that ends in 0
Round UpGoing to the next higher ten or hundred
Round DownGoing to the lower ten or hundred
ReasonableAn answer that makes sense and is close to the estimate

Mathematics -- Class 4 (continued)

Topic: Estimation and Rounding -- Key Points and Practice
Key Points to Remember
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?

ItemActual 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?