Mathematics -- Class 3

Topic: Estimation
Name: ____________________________Class: 3Date: ________________
Learning Objectives
Let Us Begin!

Imagine your mother asks, "About how many people came to the wedding?" You might say, "About 200." You did not count every person. You made a smart guess. This smart guess is called an estimation.

Estimation helps us get a quick answer that is close to the exact answer. It is very useful in daily life!

What Is Estimation?

Estimation means finding an answer that is close to the exact answer, without doing the full calculation. It is a smart guess, not a wild guess.

We use estimation when we do not need the exact number, or when we want to quickly check if our answer makes sense.

Think about it: If a shopkeeper says 48 toffees cost 52 rupees, you can quickly estimate: 50 toffees at about 1 rupee each = about 50 rupees. That sounds about right!

Rounding to the Nearest 10

To estimate, we first need to learn rounding. Rounding means changing a number to the nearest ten to make it simpler.

Rule: Look at the ones digit (the last digit).

- If the ones digit is 5 or more (5, 6, 7, 8, 9), round up to the next ten.

- If the ones digit is less than 5 (0, 1, 2, 3, 4), round down to the previous ten.

Examples of Rounding to the Nearest 10
NumberOnes Digit5 or More? Less than 5?Rounded to Nearest 10
233Less than 5 -- round down20
4775 or more -- round up50
3555 or more -- round up40
611Less than 5 -- round down60
8885 or more -- round up90
144Less than 5 -- round down10
Using Estimation to Check Addition

After solving an addition problem, you can use estimation to check if your answer is reasonable.

Example: Checking Addition

Problem: 38 + 43 = ?

Step 1: Round each number to the nearest 10. 38 rounds to 40. 43 rounds to 40.

Step 2: Add the rounded numbers. 40 + 40 = 80.

Step 3: The exact answer is 81. The estimate is 80. They are close, so the answer is reasonable.

Key Words and Meanings
WordMeaning
EstimationA smart guess that is close to the exact answer
RoundingChanging a number to the nearest ten to make it simpler
Round upGo to the next higher ten (when ones digit is 5 or more)
Round downGo to the previous lower ten (when ones digit is less than 5)
ReasonableAn answer that makes sense and is close to the estimate

Mathematics -- Class 3 (continued)

Topic: Estimation -- Key Points and Practice
Using Estimation to Check Subtraction
Example: Checking Subtraction

Problem: 74 - 29 = ?

Step 1: Round each number. 74 rounds to 70. 29 rounds to 30.

Step 2: Subtract the rounded numbers. 70 - 30 = 40.

Step 3: The exact answer is 45. The estimate is 40. They are close, so the answer is reasonable.

Key Points to Remember
Practice Questions

A. Round each number to the nearest 10.

  1. 26 rounds to
  2. 53 rounds to
  3. 45 rounds to
  4. 71 rounds to
  5. 89 rounds to
  6. 34 rounds to

B. Estimate by rounding to the nearest 10, then add or subtract.

  1. 42 + 37: Estimate: + =
  2. 56 + 28: Estimate: + =
  3. 83 - 47: Estimate: - =
  4. 65 - 21: Estimate: - =

C. Multiple Choice Questions

  1. What is 67 rounded to the nearest 10?
    (a) 60(b) 65(c) 70(d) 80
  2. Ravi says 48 + 33 is about 80. Is his estimate reasonable?
    (a) Yes(b) No
  3. When rounding 52 to the nearest 10, we round __________.
    (a) up to 60(b) down to 50(c) up to 55(d) down to 40

D. Short Answer

  1. Priya solved 57 + 36 and got 93. Estimate to check if her answer is reasonable. Show your work.
  2. A shopkeeper had 82 apples. He sold 39. He says 53 are left. Use estimation to check.
Think and Do -- Estimation Jar

Estimation Jar Activity: Your teacher will show you a jar filled with objects (like beads, buttons, or seeds). Without counting, write your smart guess below. Then count the actual number and see how close your estimate was!

Object in the JarMy Estimate (Smart Guess)Actual CountHow Close Was I?
Round 1:
Round 2:
Round 3:

Tip: Look at a small group first, count it, then estimate how many such groups fill the jar.