Open Sentences, Open Sentences Involving Addition of Numbers for Primary 3

Class: Primary 3
Term: First Term
Week: 7
Age: 8 years
Duration: 45 minutes
Subject: Mathematics
Curriculum Theme: Mathematics
Previous Lesson: Subtraction of 3-Digit Numbers.
Topic: Open Sentences
Subject Matter: Open sentences involving addition of numbers, Open sentences involving subtraction of numbers

Specific Objectives

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

Cognitive Domain:

• Identify open sentences.
• Find missing numbers in open sentences involving addition, such as 9 + ___ = 15.
• Find missing numbers in open sentences involving subtraction, such as 18 – ___ = 7.
• Understand the relationship between addition and subtraction in solving open sentences.
• Solve simple quantitative aptitude problems involving open sentences.

Affective Domain:

• Appreciate the relationship between addition and subtraction.
• Develop an interest in solving mathematical problems.

Psychomotor Domain:

• Correctly write and solve open sentences.
• Demonstrate how to find missing numbers in given open sentences.

Social Domain:

• Give examples of open sentences from everyday life.

Reference Materials

The following resources were used in planning this lesson:

• 9 Years Basic Education Curriculum
• State Unified Scheme of Work
• New General Mathematics for Primary Schools 3

Instructional Materials

The teacher will teach this lesson with the aid of:

• Whiteboard or blackboard
• Markers or chalk
• Flashcards with open sentences (e.g., 5 + ? = 12)
• Number charts

Rationale for the Lesson

This lesson helps pupils understand basic algebraic concepts by finding missing numbers in simple equations. It enables them to appreciate the inverse relationship between addition and subtraction, which is important for developing problem-solving skills in mathematics and everyday situations.

Prerequisite/Previous Knowledge

Pupils have prior knowledge of basic addition and subtraction of numbers.

Lesson Content/Board Summary

Open Sentences

Open Sentences Involving Addition

An open sentence is a mathematical statement that contains an unknown value, represented by a symbol (like a box or a letter). To solve an open sentence, we find the value of the unknown that makes the statement true.

To find the missing number in an addition open sentence, we subtract the known number from the sum (total).

Example 1: Find the missing number in 9 + ___ = 15

• Step 1: Identify the sum and the known number. (Sum = 15, Known number = 9)
• Step 2: Subtract the known number from the sum. 15 – 9 = 6
• Step 3: The missing number is 6. So, 9 + 6 = 15.

Example 2: What number should be in the box: ___ + 7 = 13

• Step 1: Identify the sum and the known number. (Sum = 13, Known number = 7)
• Step 2: Subtract the known number from the sum. 13 – 7 = 6
• Step 3: The missing number is 6. So, 6 + 7 = 13.

Open Sentences Involving Subtraction

To find the missing number in a subtraction open sentence, the method depends on where the missing number is located.

Case 1: Missing number is the subtrahend (the number being subtracted).

To find the missing number, subtract the result from the first number.

Example 1: Find the missing number in 18 – ___ = 7

• Step 1: Identify the first number and the result. (First number = 18, Result = 7)
• Step 2: Subtract the result from the first number. 18 – 7 = 11
• Step 3: The missing number is 11. So, 18 – 11 = 7.

Case 2: Missing number is the minuend (the first number).

To find the missing number, add the known number (subtrahend) to the result.

Example 2: What number should be in the box: ___ – 5 = 10

• Step 1: Identify the known number (subtrahend) and the result. (Known number = 5, Result = 10)
• Step 2: Add the known number to the result. 10 + 5 = 15
• Step 3: The missing number is 15. So, 15 – 5 = 10.

Relationship between Addition and Subtraction

Addition and subtraction are inverse operations. This means they undo each other. We use this relationship to find missing numbers in open sentences.

• If you have an addition problem with a missing number, you can use subtraction to find it.
• If you have a subtraction problem with a missing number, you can use addition or subtraction (depending on the position) to find it.

Everyday Examples of Open Sentences

Open sentences are used to solve problems in daily life. For example:

• “I had 10 mangoes, I ate some, and now I have 7 left. How many did I eat?” (10 – ___ = 7)
• “My friend gave me some pencils, and I already had 5. Now I have 12 pencils. How many did my friend give me?” (___ + 5 = 12)

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Open Sentences

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and reviews the previous lesson on simple addition and subtraction. The teacher then introduces the topic “Open Sentences” by asking pupils to think about puzzles where something is missing.
Pupils’ Activity: Pupils respond to greetings, recall previous knowledge, and listen attentively to the introduction.
Learning Point: Pupils are prepared for the new lesson and understand its relevance.

Step 2: Explanation of Open Sentences Involving Addition

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines an open sentence and explains how to find missing numbers in addition problems using subtraction, demonstrating with examples like 9 + ___ = 15 on the board.
Pupils’ Activity: Pupils listen to the explanation, ask questions for clarification, and observe the examples on the board.
Learning Point: Pupils understand the concept of open sentences and how to solve addition-based ones.

Step 3: Guided Practice (Addition)

Time: 5 minutes
Teaching Skill: Guided Practice
Teacher’s Activity: The teacher writes more addition open sentences on the board (e.g., 7 + ___ = 10, ___ + 4 = 11) and guides pupils to solve them, calling on individuals to explain their steps.
Pupils’ Activity: Pupils participate by solving the problems orally and on their slates/notebooks, explaining their methods.
Learning Point: Pupils reinforce their understanding and practice solving addition open sentences.

Step 4: Explanation of Open Sentences Involving Subtraction

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains how to find missing numbers in subtraction problems, covering both cases (missing subtrahend and missing minuend) with examples like 18 – ___ = 7 and ___ – 5 = 10.
Pupils’ Activity: Pupils pay attention to the different methods for solving subtraction open sentences and ask relevant questions.
Learning Point: Pupils learn how to solve subtraction-based open sentences based on the position of the missing number.

Step 5: Guided Practice (Subtraction)

Time: 5 minutes
Teaching Skill: Guided Practice
Teacher’s Activity: The teacher provides additional subtraction open sentences (e.g., 15 – ___ = 8, ___ – 6 = 9) for pupils to solve, offering support and correcting misconceptions.
Pupils’ Activity: Pupils attempt to solve the problems, demonstrating their understanding and applying the learned methods.
Learning Point: Pupils consolidate their skills in solving subtraction open sentences.

Step 6: Real-life Examples and Quantitative Aptitude

Time: 5 minutes
Teaching Skill: Application/Problem-Solving
Teacher’s Activity: The teacher discusses real-life scenarios where open sentences can be used and presents simple quantitative aptitude questions related to finding missing numbers.
Pupils’ Activity: Pupils provide their own real-life examples and attempt to solve the quantitative aptitude problems.
Learning Point: Pupils connect open sentences to practical situations and develop problem-solving abilities.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is an open sentence?
2. Find the missing number in 10 + ___ = 17.
3. Find the missing number in 20 – ___ = 12.
4. What is the missing number in ___ – 7 = 13?
5. Give one everyday example of an open sentence.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 1 minute
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, emphasizing the relationship between addition and subtraction in solving open sentences. The teacher assigns homework.
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their learning and are prepared for further practice.

Home Task: Solve three new exercises on Open Sentences. Show each step and check each answer.

Lesson Keywords

• Open sentence – A mathematical statement with an unknown value.
• Missing number – The unknown value in an open sentence.
• Addition – The process of combining numbers.
• Subtraction – The process of taking one number away from another.
• Equation – A statement that two mathematical expressions are equal.

Differentiation

For struggling learners, the teacher will provide simpler examples with smaller numbers and offer one-on-one support. Advanced learners will be given more complex open sentences or multi-step quantitative aptitude problems to solve independently or in small groups.

Note for teachers using this lesson plan

Ensure that pupils clearly understand the inverse relationship between addition and subtraction before proceeding to solve open sentences. Use visual aids like number lines or counters to demonstrate the concepts, especially for subtraction open sentences where the missing number can be in different positions. Encourage pupils to create their own open sentences and real-life scenarios to enhance understanding.