Addition and subtraction of lengths for Primary 4

Class: Primary 4
Term: Third Term
Week: 2
Age: 9 years
Duration: 45 minutes
Subject: General Mathematics
Curriculum Theme: Mensuration
Focal competence: Calculating length and distance in kilometers, meters and centimeters
Key competencies/values: Communication; ICT and Digital Competencies
Skills:

• Estimating and calculating the length of a distance

Previous Lesson: Estimating and Measuring Distances and Lengths
Topic: Length: Addition And Subtraction
Subject Matter: Addition and subtraction of lengths

Specific Objectives

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

Cognitive Domain

• Add lengths correctly.
• Subtract lengths accurately.

Affective Domain

• Appreciate the importance of accurate measurement in real-life situations.
• Show carefulness when aligning units for calculation.

Psychomotor Domain

• Demonstrate the addition of lengths using measuring tools.
• Demonstrate the subtraction of lengths using measuring tools.

Social Domain

• Collaborate with peers to solve length-related word problems.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Universal Basic Education (UBE) Mathematics for Primary 4
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Tape
• Meter rule
• Ruler
• Chart showing examples of addition and subtraction of lengths

Rationale for the Lesson

This lesson is important as it equips pupils with fundamental skills in mensuration, which are essential for everyday tasks. Understanding how to add and subtract lengths helps pupils solve practical problems related to distances, construction, and design. It builds a strong foundation for more complex mathematical concepts involving measurements.

Prerequisite/Previous Knowledge

Pupils should have a basic understanding of different units of length (centimeters, meters, kilometers) and be able to perform simple addition and subtraction of whole numbers.

Lesson Content/Board Summary

Length: Addition And Subtraction

Addition of Lengths

Adding lengths involves combining two or more measurements of length to find a total length. It is important to align the units (e.g., centimeters with centimeters, meters with meters) before adding. If the units are different, convert them to a common unit first.

Steps for Adding Lengths

1. Write the lengths, aligning the units vertically.
2. Add the numbers in each unit column, starting from the smallest unit (e.g., cm before m).
3. If the sum in a smaller unit column exceeds its conversion value (e.g., 100 cm = 1 m), carry over to the next larger unit.

Example 1

Question: Add 3 m 45 cm and 2 m 30 cm.

Solution:

Step 1: Write the lengths, aligning units.

( quad 3 text{ m } 45 text{ cm} )
( underline{+ 2 text{ m } 30 text{ cm}} )

Step 2: Add the cm column.

( 45 text{ cm} + 30 text{ cm} = 75 text{ cm} )

Step 3: Add the m column.

( 3 text{ m} + 2 text{ m} = 5 text{ m} )

Answer: ( 5 text{ m } 75 text{ cm} )

Example 2

Question: A tailor used 1 m 75 cm of fabric for a shirt and 2 m 50 cm for a pair of trousers. What is the total length of fabric used?

Solution:

Step 1: Write the lengths, aligning units.

( quad 1 text{ m } 75 text{ cm} )
( underline{+ 2 text{ m } 50 text{ cm}} )

Step 2: Add the cm column.

( 75 text{ cm} + 50 text{ cm} = 125 text{ cm} )

Step 3: Convert 125 cm to m and cm (since 100 cm = 1 m).

( 125 text{ cm} = 1 text{ m } 25 text{ cm} )

Step 4: Add the m column, including the carried-over meter.

( 1 text{ m} + 2 text{ m} + 1 text{ m (carried over)} = 4 text{ m} )

Answer: ( 4 text{ m } 25 text{ cm} )

Subtraction of Lengths

Subtracting lengths involves finding the difference between two measurements of length. Just like addition, units must be aligned. If a smaller unit needs to be subtracted from a larger one, you may need to ‘borrow’ from the next larger unit.

Steps for Subtracting Lengths

1. Write the lengths, aligning the units vertically.
2. Subtract the numbers in each unit column, starting from the smallest unit.
3. If the number in the top row of a unit column is smaller than the number below it, borrow from the next larger unit. Remember the conversion (e.g., 1 m = 100 cm).

Example 1

Question: Subtract 1 m 20 cm from 4 m 50 cm.

Solution:

Step 1: Write the lengths, aligning units.

( quad 4 text{ m } 50 text{ cm} )
( underline{- 1 text{ m } 20 text{ cm}} )

Step 2: Subtract the cm column.

( 50 text{ cm} – 20 text{ cm} = 30 text{ cm} )

Step 3: Subtract the m column.

( 4 text{ m} – 1 text{ m} = 3 text{ m} )

Answer: ( 3 text{ m } 30 text{ cm} )

Example 2

Question: A rope is 5 m 30 cm long. If 2 m 70 cm is cut off, what length of rope is left?

Solution:

Step 1: Write the lengths, aligning units.

( quad 5 text{ m } 30 text{ cm} )
( underline{- 2 text{ m } 70 text{ cm}} )

Step 2: Subtract the cm column. (Since 30 cm is less than 70 cm, we need to borrow).

Step 3: Borrow 1 m from 5 m, which becomes 4 m. Convert the borrowed 1 m to 100 cm and add to 30 cm.

( 100 text{ cm} + 30 text{ cm} = 130 text{ cm} )

Step 4: Now subtract the cm column.

( 130 text{ cm} – 70 text{ cm} = 60 text{ cm} )

Step 5: Subtract the m column (remember 5 m became 4 m).

( 4 text{ m} – 2 text{ m} = 2 text{ m} )

Answer: ( 2 text{ m } 60 text{ cm} )

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Problem Solving, Individual Practice

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Recalling/Engaging

Teacher’s Activity: The teacher greets the pupils and asks them to name different units of length they know (e.g., cm, m, km). The teacher then reminds them that they have learned about measuring lengths.

Pupils’ Activity: Pupils respond by naming units of length and recalling previous lessons on measurement.

Learning Point: Recall of length units

Step 2: Explanation of Addition of Lengths

Time: 7 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains how to add lengths, emphasizing the importance of aligning units (cm under cm, m under m). The teacher uses a chart to show a simple example without borrowing.

Pupils’ Activity: Pupils listen attentively and observe the example on the chart.

Learning Point: Rules for adding lengths

Step 3: Guided Practice (Addition)

Time: 7 minutes

Teaching Skill: Modelling/Guided Practice

Teacher’s Activity: The teacher models another addition problem, including one that involves carrying over from cm to m, using the board and explaining each step clearly. For example, adding 1 m 80 cm and 2 m 40 cm.

Pupils’ Activity: Pupils follow along, asking questions for clarification, and attempt to solve the problem with the teacher’s guidance.

Learning Point: Practical length addition

Step 4: Independent Practice (Addition)

Time: 5 minutes

Teaching Skill: Problem Solving/Application

Teacher’s Activity: The teacher gives pupils a simple addition problem involving lengths to solve individually or in pairs. For example, “Add 4 m 25 cm and 1 m 60 cm.” The teacher walks around to provide support.

Pupils’ Activity: Pupils solve the given addition problem in their notebooks.

Learning Point: Applying length addition

Step 5: Explanation of Subtraction of Lengths

Time: 7 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains how to subtract lengths, again stressing unit alignment. The teacher shows a simple subtraction example on the chart, without borrowing.

Pupils’ Activity: Pupils listen and observe the subtraction example.

Learning Point: Rules for subtracting lengths

Step 6: Guided Practice (Subtraction)

Time: 7 minutes

Teaching Skill: Modelling/Guided Practice

Teacher’s Activity: The teacher models a subtraction problem that involves borrowing from meters to centimeters (e.g., Subtract 1 m 80 cm from 3 m 50 cm), explaining the borrowing process clearly.

Pupils’ Activity: Pupils follow the steps, asking questions, and try to solve the problem with the teacher.

Learning Point: Practical length subtraction

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. Add 5 m 15 cm and 3 m 40 cm.
2. Subtract 2 m 10 cm from 7 m 35 cm.
3. A ribbon is 6 m long. If 2 m 80 cm is used, how much is left?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Assessment of length operations

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils to copy the essential Board Summary notes on addition and subtraction of lengths, including the worked examples, into their notebooks.

Pupils’ Activity: Pupils copy the notes carefully into their notebooks.

Learning Point: Recording lesson notes

Step 9: Conclusion

Time: 3 minutes

Teaching Skill: Consolidation

Teacher’s Activity: The teacher briefly reminds pupils about the importance of aligning units when adding or subtracting lengths and encourages them to practice more at home. The teacher praises their participation.

Pupils’ Activity: Pupils listen and acknowledge the importance of practice.

Learning Point: Reinforcement of concepts

Continuous Assessment/Further Study

Type: Homework

Instruction: Solve the following problems in your mathematics notebook:

1. Add: 4 km 200 m + 3 km 500 m
2. Subtract: 8 m 90 cm – 3 m 40 cm
3. A carpenter needs two pieces of wood. One is 1 m 60 cm long, and the other is 2 m 75 cm long. What is the total length of wood needed?
4. A road is 10 km long. If 3 km 450 m has been repaired, what length of the road is left to be repaired?

Lesson Keywords

• Length – The measurement or extent of something from end to end.
• Add – To combine numbers or quantities to get a total.
• Subtract – To take away one number or quantity from another.
• Centimeter (cm) – A unit of length, equal to one hundredth of a meter.
• Meter (m) – The basic unit of length in the metric system.
• Kilometer (km) – A unit of length equal to 1,000 meters.
• Align – To arrange in a straight line or in correct relative positions.

Differentiation

For weaker learners, provide additional practice with simpler problems involving only one unit (e.g., adding cm only, then adding m only). Use physical measuring tools for hands-on practice. For faster learners, introduce more complex word problems or problems involving three lengths, or challenge them to convert between units before adding/subtracting.

Suggested Lesson Videos

Search YouTube for: “Primary 4 addition and subtraction of lengths”

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure you have your measuring tools (ruler, meter rule, tape) and a pre-prepared chart with clear examples of addition and subtraction of lengths. Start by reviewing units of length to activate prior knowledge. When teaching, emphasize the critical step of aligning units correctly. Model both addition and subtraction, particularly focusing on examples that involve carrying over or borrowing across different units (e.g., cm to m). Allow ample time for guided practice and individual problem-solving. During the evaluation stage, assess both understanding of the concept and accuracy in calculation. Ensure pupils copy the Board Summary notes carefully, as these will serve as a valuable reference. Encourage pupils to use their understanding of length operations in real-world contexts.