Addition and Subtraction of Approximations (JSS 1 Mathematics Lesson Note)
Lesson Plan: Addition and Subtraction of Approximations
Subject: Mathematics
Class: JSS 1
Term: Second Term
Week: 3
Age: 10–12 years
Topic: Addition and Subtraction of Approximations
Sub-topic: Rounding Off Numbers Before Performing Arithmetic Operations
Duration: 40 minutes
Behavioural Objectives
By the end of the lesson, students should be able to:
- Define approximation in relation to addition and subtraction.
- Round off numbers to a required decimal place or significant figure before calculation.
- Add and subtract approximated numbers correctly.
- Solve real-life problems using addition and subtraction of approximated numbers.
Keywords
- Approximation
- Rounding off
- Decimal places
- Significant figures
- Estimation
- Accuracy
Set Induction
The teacher presents two numbers (e.g., 67.345 and 45.678) and asks students:
- “What happens if we round these numbers before adding them?”
- “Why do we sometimes round numbers before calculating?”
This prompts students to think about approximation before performing operations.
Entry Behaviour
Students have learned how to round numbers to decimal places and significant figures. They also know basic addition and subtraction operations.
Learning Resources and Materials
- Number charts
- Flashcards with decimal and whole numbers
- Whiteboard and marker
- Real-life scenarios (e.g., estimating grocery costs)
Building Background/Connection to Prior Knowledge
The teacher reminds students of the previous lesson on approximation and rounding off numbers. The teacher asks:
- “How do we round 23.678 to 2 decimal places?”
- “What is 56.78 rounded to the nearest whole number?”
This helps students recall rounding techniques before moving to addition and subtraction.
Embedded Core Skills
- Critical thinking
- Problem-solving
- Application of mathematical skills in real life
Learning Materials
- Lagos State Scheme of Work
- Essential Mathematics for JSS 1
- New General Mathematics for Junior Secondary Schools
Instructional Materials
- Chart showing rules of rounding off
- Flashcards with practice numbers
- Workbooks for calculations
Content (Explanation in List Format)
1. Meaning of Addition and Subtraction of Approximations
- Approximation means rounding numbers to make calculations easier.
- We can round to the nearest whole number, decimal place, or significant figure.
- After rounding, we perform addition or subtraction.
2. Steps for Adding and Subtracting Approximated Numbers
- Identify the required degree of approximation (decimal places or significant figures).
- Round each number before performing the operation.
- Add or subtract the rounded numbers.
- Compare the approximated result with the actual result.
3. Examples of Addition and Subtraction of Approximations
Example 1: Addition of Approximations
Question: Add 56.478 and 23.645, correct to 1 decimal place.
Solution:
- 56.478 ≈ 56.5 (to 1 d.p)
- 23.645 ≈ 23.6 (to 1 d.p)
- 56.5 + 23.6 = 80.1
Example 2: Subtraction of Approximations
Question: Subtract 45.768 from 89.342, correct to 2 decimal places.
Solution:
- 89.342 ≈ 89.34 (to 2 d.p)
- 45.768 ≈ 45.77 (to 2 d.p)
- 89.34 – 45.77 = 43.57
Example 3: Real-Life Scenario
A trader estimates the total cost of ₦198.75 and ₦134.65 before payment. She rounds both numbers to the nearest whole number and adds them.
- ₦198.75 ≈ ₦199
- ₦134.65 ≈ ₦135
- ₦199 + ₦135 = ₦334
Evaluation (10 Fill-in-the-Blank Questions with Options)
-
Approximation is the process of ______ numbers for easy calculation.
a) rounding off
b) increasing
c) deleting
d) multiplying -
34.789 rounded to 2 decimal places is ______.
a) 34.8
b) 34.79
c) 34.78
d) 34.7 -
98.56 rounded to the nearest whole number is ______.
a) 98
b) 99
c) 100
d) 97 -
45.67 – 12.34 rounded to 1 decimal place is ______.
a) 33.3
b) 33.4
c) 34.5
d) 34.6 -
The first step in adding approximations is to ______.
a) round off numbers
b) subtract first
c) multiply first
d) ignore decimals -
76.48 + 32.91 rounded to 1 decimal place is ______.
a) 109.4
b) 109.5
c) 109.3
d) 109.0 -
15.679 rounded to 2 significant figures is ______.
a) 15.7
b) 16
c) 15.6
d) 15.68 -
99.87 – 56.12 rounded to 1 decimal place is ______.
a) 43.8
b) 43.7
c) 43.6
d) 43.9 -
42.765 rounded to the nearest whole number is ______.
a) 42
b) 43
c) 44
d) 41 -
67.45 + 32.64 correct to 1 decimal place is ______.
a) 100.1
b) 100.0
c) 100.2
d) 99.9
Class Activity Discussion (10 FAQs with Answers)
-
What is approximation?
- Approximation is rounding off numbers to make calculations simpler.
-
Why do we approximate numbers before addition or subtraction?
- To make calculations faster and easier.
-
What is the difference between decimal places and significant figures?
- Decimal places count digits after the decimal, while significant figures count all important digits.
-
How do I know when to round up or down?
- If the next digit is 5 or more, round up; otherwise, round down.
-
Can approximation affect the accuracy of an answer?
- Yes, but it provides a close estimate.
-
What is 56.432 rounded to 2 decimal places?
- 56.43.
-
Why is estimation useful in real life?
- It helps in budgeting, measuring, and planning.
-
What is 76.89 + 23.56 to the nearest whole number?
- 101.
-
What happens if we don’t approximate numbers in calculations?
- The calculations may be more complex.
-
Is 1.999 rounded to the nearest whole number equal to 2?
- Yes.
Presentation Steps
- Teacher revises previous topics on approximation.
- Teacher explains addition and subtraction of approximations.
- Teacher demonstrates with examples.
- Students practice in groups.
- Teacher reviews students’ answers and corrects mistakes.
Conclusion
- The teacher summarizes the lesson and gives additional exercises.
- Students explain their answers to real-life approximation problems.
- The teacher marks students’ work and provides feedback.