Class: Primary 4 (Pry 4)
Term: 2nd Term
Week: 6
Age: 9 years
Duration: 45 minutes
Subject: General Mathematics
Curriculum Theme: Measurement
Previous Lesson: Length, Units, Estimation and Actual Measurement.
Topic: LENGTH (Continued)
Subject Matter: Addition of length in mixed units, subtraction of length in mixed units, word problems on addition of lengths, word problems on subtraction of lengths, quantitative reasoning involving addition and subtraction of length.

Specific Objectives

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

Cognitive Domain:

Add lengths expressed in mixed units.
Subtract lengths expressed in mixed units.
Solve word problems involving addition of lengths.
Solve word problems involving subtraction of lengths.
Solve quantitative reasoning problems on addition and subtraction of length.

Affective Domain:

Appreciate the importance of accurate measurement in daily life.
Participate actively in solving length problems.

Psychomotor Domain:

Correctly set out and calculate sums involving mixed units of length.
Accurately record solutions to word problems and quantitative reasoning.

Discuss solutions to length problems with peers.
Collaborate with classmates to solve challenging problems.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum, Primary 4 General Mathematics.
State Unified Scheme of Work, Primary 4 General Mathematics.
New General Mathematics for Primary Schools, Book 4.
Pupil’s workbook.

Instructional Materials

The teacher will teach this lesson with the aid of:

Textbook
Workbook
Measuring tape
Ruler
Chart showing units of length conversion (e.g., 1 m = 100 cm).

Rationale for the Lesson

Understanding how to add and subtract lengths in mixed units helps pupils solve real-life problems involving measurements. This lesson enables pupils to accurately calculate distances, sizes, and quantities encountered daily, which is important for practical situations.

Prerequisite/Previous Knowledge

Pupils can identify different units of length (metres, centimetres) and perform basic addition and subtraction of whole numbers. They also know how to convert between simple units of length.

Lesson Content/Board Summary

LENGTH: Addition and Subtraction in Mixed Units

Addition of Length in Mixed Units

Adding lengths in mixed units means combining measurements that have different units, such as metres and centimetres. It is important to add units of the same kind together.

To add lengths in mixed units:

Arrange the lengths in columns, with metres under metres and centimetres under centimetres.
Add the centimetres first.
If the sum of centimetres is 100 or more, convert 100 cm to 1 m and carry over to the metres column.
Add the metres.

Example: Add 3 m 45 cm and 2 m 70 cm.

    m   cm
    3   45
+   2   70
---------
    6   15  (45 + 70 = 115 cm = 1 m 15 cm; carry over 1 m)

Subtraction of Length in Mixed Units

Subtracting lengths in mixed units means finding the difference between two measurements that have different units. It is important to subtract units of the same kind.

To subtract lengths in mixed units:

Arrange the lengths in columns, with metres under metres and centimetres under centimetres.
Subtract the centimetres first.
If the number of centimetres to be subtracted is larger than the available centimetres, borrow 1 metre (100 cm) from the metres column and add it to the centimetres column.
Subtract the metres.

Example: Subtract 1 m 80 cm from 5 m 20 cm.

    m   cm
    5   20  (Borrow 1 m from 5 m, convert to 100 cm and add to 20 cm => 4 m 120 cm)
-   1   80
---------
    3   40  (120 - 80 = 40 cm; 4 - 1 = 3 m)

Word Problems on Addition and Subtraction of Lengths

Word problems require careful reading to determine if addition or subtraction is needed. Look for keywords like “total,” “altogether,” “sum” for addition, and “difference,” “left,” “remaining,” “how much more/less” for subtraction.

Example (Addition): A rope is 4 m 60 cm long. Another rope is 3 m 75 cm long. What is the total length of the two ropes?

Solution: 4 m 60 cm + 3 m 75 cm = 8 m 35 cm

Example (Subtraction): A tailor had 7 m 25 cm of fabric. She used 3 m 50 cm to make a dress. How much fabric is left?

Solution: 7 m 25 cm – 3 m 50 cm = 3 m 75 cm

Quantitative Reasoning Involving Addition and Subtraction of Length

Quantitative reasoning involves solving problems by applying mathematical concepts and operations. For length, this might include completing number patterns or solving simple puzzles using addition and subtraction of mixed units.

Example: Complete the sequence: 1 m 20 cm, 2 m 40 cm, _____, 4 m 80 cm.

Solution: The pattern adds 1 m 20 cm each time. So, 2 m 40 cm + 1 m 20 cm = 3 m 60 cm.

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 length conversion. The teacher then introduces the new topic, “Length: Addition and Subtraction in Mixed Units,” by asking pupils if they have ever needed to combine or find the difference between two lengths, such as the length of two tables or the remaining part of a fabric.
Pupils’ Activity: Pupils respond to questions and listen attentively to the teacher.
Learning Point: Pupils recall prior knowledge and are prepared for the new lesson.

Step 2: Addition of Length in Mixed Units

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains how to add lengths in mixed units, emphasizing arranging units in columns and carrying over when centimetres exceed 100. The teacher demonstrates with the example: Add 3 m 45 cm and 2 m 70 cm. The teacher then provides one or two practice problems for pupils to solve on their own.
Pupils’ Activity: Pupils listen, observe the demonstration, ask questions, and solve practice problems in their notebooks.
Learning Point: Pupils learn the steps for adding lengths in mixed units.

Step 3: Subtraction of Length in Mixed Units

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains how to subtract lengths in mixed units, focusing on borrowing from the metres column when needed. The teacher demonstrates with the example: Subtract 1 m 80 cm from 5 m 20 cm. The teacher provides practice problems for pupils to work on.
Pupils’ Activity: Pupils pay attention, observe, ask questions, and practice solving subtraction problems.
Learning Point: Pupils learn the steps for subtracting lengths in mixed units.

Step 4: Word Problems on Addition of Length

Time: 5 minutes
Teaching Skill: Problem-solving/Guidance
Teacher’s Activity: The teacher guides pupils on how to identify word problems that require addition of length. The teacher presents an addition word problem (e.g., “A rope is 4 m 60 cm long. Another rope is 3 m 75 cm long. What is the total length of the two ropes?”) and guides pupils through the solution.
Pupils’ Activity: Pupils identify keywords, participate in solving the problem, and write down the solution.
Learning Point: Pupils can solve word problems involving addition of lengths.

Step 5: Word Problems on Subtraction of Length

Time: 5 minutes
Teaching Skill: Problem-solving/Guidance
Teacher’s Activity: The teacher guides pupils on how to identify word problems that require subtraction of length. The teacher presents a subtraction word problem (e.g., “A tailor had 7 m 25 cm of fabric. She used 3 m 50 cm to make a dress. How much fabric is left?”) and guides pupils through the solution.
Pupils’ Activity: Pupils identify keywords, participate in solving the problem, and write down the solution.
Learning Point: Pupils can solve word problems involving subtraction of lengths.

Step 6: Quantitative Reasoning Involving Length

Time: 5 minutes
Teaching Skill: Critical Thinking/Application
Teacher’s Activity: The teacher introduces simple quantitative reasoning problems related to length, such as completing a pattern or solving a simple puzzle involving addition/subtraction of mixed units. The teacher provides an example and guides pupils to find the solution.
Pupils’ Activity: Pupils observe, think critically, and attempt to solve the quantitative reasoning problem.
Learning Point: Pupils apply their knowledge of length operations to solve 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 are mixed units of length?
Add 5 m 30 cm and 2 m 80 cm.
Subtract 3 m 40 cm from 8 m 10 cm.
A tailor used 2 m 75 cm of fabric for a dress and 1 m 50 cm for a skirt. How much fabric did she use in total?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the methods for adding and subtracting lengths in mixed units and solving related word problems and quantitative reasoning. The teacher then assigns homework from the textbook or workbook.
Pupils’ Activity: Pupils listen to the summary and copy down the assigned homework.
Learning Point: Pupils reinforce their understanding and prepare for independent practice.

Home Task: Solve three new exercises on LENGTH (Continued). Show each step and check each answer.

Lesson Keywords

Length – The measurement or extent of something from end to end.
Mixed Units – Units of measurement that combine two or more different units, such as metres and centimetres.
Addition – The process of combining numbers or quantities.
Subtraction – The process of taking one number or quantity away from another.
Quantitative Reasoning – The ability to understand and use numerical data and mathematical concepts to solve problems.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide more complex word problems or multi-step quantitative reasoning tasks. For pupils who need additional support, the teacher can provide simpler examples, use visual aids like rulers or measuring tapes for hands-on practice, and offer one-on-one guidance during practice sessions.

Note for teachers using this lesson plan

Ensure pupils have a solid understanding of basic length conversions (e.g., 1 m = 100 cm) before starting this lesson. Use real-life examples to make the lesson relatable and practical. Encourage pupils to show all their working steps clearly, especially when borrowing or carrying over units. Provide ample practice opportunities for both addition and subtraction, including word problems.