Class: Primary 1
Term: 1st Term
Week: 9
Age: 6 years
Duration: 45 minutes
Subject: Mathematics
Curriculum Theme: Mathematics
Previous Lesson: Fraction, Introduction to the Concept of Fraction as Part.
Topic: Addition and Subtraction
Subject Matter: Finding missing numbers in open sentences

Specific Objectives

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

Cognitive Domain:

Understand and differentiate between increasing and decreasing numbers.
Solve problems on open sentences by finding the missing numbers.

Affective Domain:

Participate actively in solving problems involving missing numbers.
Show interest in finding missing numbers in mathematical statements.

Psychomotor Domain:

Write out simple open sentences correctly.
Fill in the correct missing numbers in given open sentences.

Work cooperatively with classmates to solve open sentence problems.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Primary 1 Mathematics
State Unified Scheme of Work
New General Mathematics for Primary Schools, Book 1

Instructional Materials

The teacher will teach this lesson with the aid of:

Number cards
Counters (e.g., bottle tops, stones)
Flashcards with open sentences
Whiteboard and markers

Rationale for the Lesson

This lesson helps pupils develop logical thinking and problem-solving skills in mathematics. Understanding how to find missing numbers lays a foundation for more complex algebraic concepts in later grades and helps pupils make sense of numerical relationships in everyday situations.

Prerequisite/Previous Knowledge

Pupils have prior knowledge of basic addition and subtraction of numbers up to 20.

Lesson Content/Board Summary

Addition and Subtraction

Finding Missing Numbers in Open Sentences

An open sentence is a number sentence that has a missing number.

Increasing and Decreasing Numbers:

When we add, numbers usually **increase** (get bigger).
When we subtract, numbers usually **decrease** (get smaller).

Finding Missing Numbers in Addition Sentences

To find a missing number in an addition sentence (e.g., 8 + (____) = 9), we can use subtraction.

Example 1: Find the missing number in 8 + (____) = 9

Step 1: We know that 8 plus a number gives 9.
Step 2: To find the missing number, we subtract 8 from 9 (9 – 8).
Step 3: 9 – 8 = 1.
The missing number is 1. So, 8 + 1 = 9.

Example 2: Find the missing number in (____) + 5 = 12

Step 1: We know that a number plus 5 gives 12.
Step 2: To find the missing number, we subtract 5 from 12 (12 – 5).
Step 3: 12 – 5 = 7.
The missing number is 7. So, 7 + 5 = 12.

Finding Missing Numbers in Subtraction Sentences

To find a missing number in a subtraction sentence (e.g., 10 – (____) = 6), we can also use subtraction.

Example 1: Find the missing number in 10 – (____) = 6

Step 1: We have 10, and we take away some number to get 6.
Step 2: To find the missing number, we subtract 6 from 10 (10 – 6).
Step 3: 10 – 6 = 4.
The missing number is 4. So, 10 – 4 = 6.

Example 2: Find the missing number in 12 – (____) = 7

Step 1: We have 12, and we take away some number to get 7.
Step 2: To find the missing number, we subtract 7 from 12 (12 – 7).
Step 3: 12 – 7 = 5.
The missing number is 5. So, 12 – 5 = 7.

Teaching Methods/Instructional Techniques

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

Instructional Procedures

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 facts. The teacher then asks simple questions like, “If I have 5 mangoes and I get 3 more, how many do I have?”
Pupils’ Activity: Pupils respond to greetings and answer the revision questions.
Learning Point: Pupils recall previous knowledge of addition and subtraction.

Step 2: Presentation of Topic

Time: 5 minutes
Teaching Skill: Explanation/Introduction
Teacher’s Activity: The teacher writes the topic “Finding Missing Numbers in Open Sentences” on the board. The teacher explains that sometimes numbers are hidden and we need to find them.
Pupils’ Activity: Pupils observe the board and listen attentively.
Learning Point: Pupils are introduced to the lesson topic.

Step 3: Explanation of Open Sentences and Number Changes

Time: 7 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains what an open sentence is using simple examples like “3 + ? = 5”. The teacher also explains that addition makes numbers increase (get bigger) and subtraction makes numbers decrease (get smaller), using counters to demonstrate.
Pupils’ Activity: Pupils listen, observe the demonstrations with counters, and repeat the terms “increase” and “decrease”.
Learning Point: Pupils understand the concept of an open sentence and how operations affect numbers.

Step 4: Finding Missing Numbers in Addition Sentences

Time: 8 minutes
Teaching Skill: Demonstration/Guided Practice
Teacher’s Activity: The teacher writes examples of addition open sentences on the board, such as 8 + (____) = 9 and (____) + 5 = 12. The teacher demonstrates how to find the missing numbers by using the inverse operation (subtraction) or counting up, guiding the pupils through each step.
Pupils’ Activity: Pupils observe the teacher’s demonstration and participate by suggesting numbers or counting along.
Learning Point: Pupils learn the method for finding missing numbers in addition problems.

Step 5: Finding Missing Numbers in Subtraction Sentences

Time: 8 minutes
Teaching Skill: Demonstration/Guided Practice
Teacher’s Activity: The teacher writes examples of subtraction open sentences on the board, such as 10 – (____) = 6 and 12 – (____) = 7. The teacher demonstrates how to find the missing numbers using subtraction, guiding pupils through the steps.
Pupils’ Activity: Pupils pay attention, observe the method, and try to solve alongside the teacher.
Learning Point: Pupils learn the method for finding missing numbers in subtraction problems.

Step 6: Class Activity/Practice

Time: 7 minutes
Teaching Skill: Group Work/Practice
Teacher’s Activity: The teacher writes a few more open sentences (both addition and subtraction) on the board or distributes flashcards. The teacher divides pupils into small groups to solve the problems, providing support as needed.
Pupils’ Activity: Pupils work in groups to solve the given open sentence problems.
Learning Point: Pupils practice and reinforce their understanding of finding missing numbers.

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?
When we add, do numbers usually increase or decrease?
Find the missing number: 6 + (____) = 10
Find the missing number: 15 – (____) = 8

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 lesson by reminding pupils that they can find missing numbers in addition and subtraction problems by thinking carefully or using subtraction. The teacher gives homework.
Pupils’ Activity: Pupils listen and copy the homework.
Learning Point: The lesson is concluded, and pupils are given practice work.

Home Task: Solve two new exercises on Addition and Subtraction. Show each step and check each answer.

Lesson Keywords

Open sentence – A number sentence with a missing number.
Missing number – The unknown number in an open sentence that needs to be found.
Addition – Putting numbers together to find a total, which makes numbers increase.
Subtraction – Taking one number away from another, which makes numbers decrease.
Increase – To get bigger in number or amount.
Decrease – To get smaller in number or amount.

Differentiation

For struggling learners, the teacher will provide more one-on-one guidance and use concrete materials like more counters for hands-on practice. Advanced learners will be given more challenging open sentences with slightly larger numbers to solve independently.

Note for teachers using this lesson plan

Ensure pupils grasp the concept of inverse operations (subtraction for addition, and vice-versa) in a simple, intuitive way for their age. Encourage the use of physical counters or drawings to help pupils visualize the process of finding missing numbers. Patience and repetition are key for this topic at Primary 1 level.