Class: Primary 4
Term: 2nd Term
Week: 2
Age: 9 years
Duration: 45 minutes
Subject: General Mathematics
Curriculum Theme: Number Operations
Previous Lesson: Estimation, Rounding Decimals and Estimating Sums and Products.
Topic: OPEN SENTENCE
Subject Matter: Open sentence in addition, open sentence in subtraction, open sentence in multiplication, open sentence in division, quantitative reasoning in open sentences.

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define an open sentence.
Solve simple open sentences involving addition.
Solve simple open sentences involving subtraction.
Solve simple open sentences involving multiplication.
Solve simple open sentences involving division.
Solve quantitative reasoning problems related to open sentences.

Affective Domain:

Appreciate the importance of finding unknown values in mathematical problems.
Show interest in solving problems involving open sentences.

Psychomotor Domain:

Accurately write down the steps to solve open sentences.
Demonstrate how to find missing numbers in various open sentence types.

Participate actively in class discussions and problem-solving activities.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Primary Schools.
State Unified Scheme of Work for Primary 4 General Mathematics.
New General Mathematics for Primary Schools, Book 4.
https://www.education.gov.ng/
https://www.nerdc.gov.ng/

Instructional Materials

The teacher will teach this lesson with the aid of:

Textbook
Workbook
Whiteboard and markers
Flashcards with simple open sentences (e.g., 5 + ? = 12)

Rationale for the Lesson

This lesson helps pupils understand how to find missing numbers in mathematical statements. This skill is important for developing logical thinking and forms a foundation for more complex algebra in higher classes, which is useful in everyday problem-solving.

Prerequisite/Previous Knowledge

Pupils can already perform basic mathematical operations such as addition, subtraction, multiplication, and division of whole numbers.

Lesson Content/Board Summary

OPEN SENTENCE

Definition of an Open Sentence

An open sentence is a mathematical statement that contains an unknown value, represented by a symbol or a letter (e.g., a box, a question mark, or a letter like ‘x’). The sentence is neither true nor false until the unknown value is found.

Examples:

3 + ? = 7
x – 5 = 10
4 × ☐ = 20

Open Sentence in Addition

To find the unknown value in an addition open sentence, we use the inverse operation, which is subtraction.

Example 1: 3 + ? = 7

Solution: ? = 7 – 3 = 4

Example 2: ? + 5 = 12

Solution: ? = 12 – 5 = 7

Open Sentence in Subtraction

To find the unknown value in a subtraction open sentence:

If the missing number is the subtrahend (the number being subtracted), subtract the result from the first number.
If the missing number is the minuend (the first number), add the subtrahend and the result.

Example 1: 8 – ? = 3

Solution: ? = 8 – 3 = 5

Example 2: ? – 4 = 6

Solution: ? = 6 + 4 = 10

Open Sentence in Multiplication

To find the unknown value in a multiplication open sentence, we use the inverse operation, which is division.

Example 1: 2 × ? = 10

Solution: ? = 10 ÷ 2 = 5

Example 2: ? × 3 = 15

Solution: ? = 15 ÷ 3 = 5

Open Sentence in Division

To find the unknown value in a division open sentence:

If the missing number is the divisor (the number dividing), divide the dividend by the result.
If the missing number is the dividend (the number being divided), multiply the divisor by the result.

Example 1: 12 ÷ ? = 4

Solution: ? = 12 ÷ 4 = 3

Example 2: ? ÷ 2 = 6

Solution: ? = 6 × 2 = 12

Quantitative Reasoning in Open Sentences

Quantitative reasoning involves using numbers and mathematical operations to solve problems or identify patterns. In open sentences, it means finding a missing number based on a given rule or pattern.

Example: Find the missing number.

(2, 4), (3, 6), (5, ?)

Solution: The rule is to multiply the first number by 2 to get the second number.

So, 5 × 2 = 10.

The missing number is 10.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 3 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them to recall what an unknown number means in simple sums like “What number added to 3 gives 7?”.
Pupils’ Activity: Pupils respond, stating that it is a number we do not know yet.
Learning Point: Pupils recall the concept of an unknown number.

Step 2: Presentation of Open Sentence

Time: 5 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher introduces the topic “Open Sentence” and explains what it means, giving examples on the board using symbols like ‘?’ or a box.
Pupils’ Activity: Pupils listen attentively and copy the definition and examples into their notebooks.
Learning Point: Pupils understand the definition of an open sentence.

Step 3: Open Sentence in Addition and Subtraction

Time: 10 minutes
Teaching Skill: Demonstration/Guided Practice
Teacher’s Activity: The teacher guides pupils to solve open sentences in addition and subtraction, explaining the use of inverse operations with clear examples on the board. For instance, 5 + ? = 10 and ? – 3 = 7.
Pupils’ Activity: Pupils follow the teacher’s explanation, ask questions, and solve similar problems presented by the teacher.
Learning Point: Pupils learn to solve open sentences involving addition and subtraction.

Step 4: Open Sentence in Multiplication

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains how to solve open sentences involving multiplication by using division (the inverse operation). The teacher provides examples like 4 × ? = 16 and ? × 2 = 14.
Pupils’ Activity: Pupils observe the examples, copy them, and attempt to solve new problems given by the teacher.
Learning Point: Pupils learn to solve open sentences involving multiplication.

Step 5: Open Sentence in Division

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains how to solve open sentences involving division, showing how to use multiplication or division depending on the position of the unknown. Examples: 18 ÷ ? = 3 and ? ÷ 5 = 4.
Pupils’ Activity: Pupils pay attention, ask questions, and solve problems from the board.
Learning Point: Pupils learn to solve open sentences involving division.

Step 6: Quantitative Reasoning in Open Sentences

Time: 6 minutes
Teaching Skill: Problem Solving/Application
Teacher’s Activity: The teacher guides pupils through simple quantitative reasoning problems related to open sentences, showing how to identify the pattern or rule to find the missing number. Example: (3, 6), (4, 8), (6, ?).
Pupils’ Activity: Pupils actively participate in finding the pattern and solving the problems.
Learning Point: Pupils apply their knowledge to solve quantitative reasoning problems.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

What is an open sentence?
Solve: 7 + ? = 15
Solve: ? – 6 = 9
Solve: 3 × ? = 21
Solve: 20 ÷ ? = 5

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarisation
Teacher’s Activity: The teacher summarizes the lesson by reiterating that an open sentence has an unknown value and can be solved using inverse operations. The teacher then assigns homework from the textbook.
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their understanding and receive further practice.

Home Task: Solve three new exercises on OPEN SENTENCE. Show each step and check each answer.

Lesson Keywords

Open sentence – A mathematical statement with an unknown value.
Unknown value – A missing number in a mathematical problem, often represented by a symbol or letter.
Inverse operation – The opposite operation used to undo another operation (e.g., subtraction is the inverse of addition, division is the inverse of multiplication).
Quantitative reasoning – Solving problems by finding patterns and rules using numbers and operations.

Differentiation

For struggling learners, the teacher will provide simpler open sentences with smaller numbers and offer one-on-one support or peer tutoring. For advanced learners, the teacher will provide more complex open sentences or multi-step quantitative reasoning problems to challenge them.

Note for teachers using this lesson plan

Ensure that pupils have a strong grasp of basic arithmetic operations before introducing open sentences. Emphasise the concept of inverse operations as a key strategy for solving these problems. Use plenty of practical examples to make the lesson relatable and engage pupils in active problem-solving.