Addition and subtraction of decimals up to three decimal places for Primary 4

Class: Primary Four
Term: First Term
Week: 10
Age: 9 years
Duration: 45 minutes
Subject: Mathematics
Curriculum Theme: Basic Operations
Focal competence: Adding and subtracting decimals
Key competencies/values: Collaboration
Skills:

• Playing decimal addition and subtraction games

Previous Lesson: Adding and subtracting mixed numbers
Topic: Addition And Subtraction Of Decimals
Subject Matter: Addition and subtraction of decimals up to three decimal places, quantitative reasoning

Specific Objectives

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

Cognitive Domain

• Perform addition of decimals up to 3 places.
• Perform subtraction of decimals up to 3 places.
• Solve quantitative aptitude problems involving addition and subtraction of decimals.

Affective Domain

• Collaborate effectively during group activities and games.
• Show accuracy and neatness when solving decimal problems.

Psychomotor Domain

• Correctly align decimal points when setting up addition and subtraction problems.
• Write out step-by-step solutions for decimal calculations clearly.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• A suitable Primary 4 Mathematics textbook
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Charts showing examples of decimal addition and subtraction
• Number cards
• Flash cards with decimal problems
• Cardboard for creating a simple decimal game
• Multimedia applications (e.g., interactive whiteboard, educational software, if available)

Rationale for the Lesson

This lesson is important as it builds on pupils’ understanding of whole numbers and introduces them to operations with decimal numbers, which are common in everyday life, such as dealing with money, measurements, and weights. Mastering these skills provides a foundation for more complex mathematical concepts and practical applications, enhancing their numerical literacy.

Prerequisite/Previous Knowledge

Pupils should have a basic understanding of whole number addition and subtraction, place values (ones, tens, hundreds), and the concept of decimals as parts of a whole.

Lesson Content/Board Summary

Addition And Subtraction Of Decimals

Understanding Decimals and Place Value

Decimals are numbers that represent parts of a whole. The decimal point separates the whole number part from the fractional part. Each digit after the decimal point has a specific place value:

1. First digit after the decimal point is the tenths place (( frac{1}{10} )).
2. Second digit after the decimal point is the hundredths place (( frac{1}{100} )).
3. Third digit after the decimal point is the thousandths place (( frac{1}{1000} )).

Rules for Adding Decimals

To add decimals:

1. Write the numbers vertically, aligning the decimal points.
2. Add zeros to the end of the shorter decimal numbers so that all numbers have the same number of decimal places.
3. Add the numbers as you would with whole numbers, starting from the rightmost digit.
4. Place the decimal point in the answer directly below the decimal points in the numbers being added.

Example 1 (Addition)

Question: Add ( 12.345 ) and ( 6.789 ).

Solution:

Step 1: Write the numbers vertically, aligning decimal points.

( begin{array}{r} 12.345 \ +quad 6.789 \ hline end{array} )

Step 2: Add the numbers from right to left.

( begin{array}{r} 12.345 \ +quad 6.789 \ hline 19.134 end{array} )

Answer: ( 19.134 )

Example 2 (Addition)

Question: Add ( 3.5 ) and ( 8.274 ).

Solution:

Step 1: Write the numbers vertically, aligning decimal points and adding zeros.

( begin{array}{r} 3.500 \ +quad 8.274 \ hline end{array} )

Step 2: Add the numbers from right to left.

( begin{array}{r} 3.500 \ +quad 8.274 \ hline 11.774 end{array} )

Answer: ( 11.774 )

Rules for Subtracting Decimals

To subtract decimals:

1. Write the numbers vertically, aligning the decimal points.
2. Add zeros to the end of the shorter decimal numbers so that all numbers have the same number of decimal places.
3. Subtract the numbers as you would with whole numbers, starting from the rightmost digit. Borrow when necessary.
4. Place the decimal point in the answer directly below the decimal points in the numbers being subtracted.

Example 1 (Subtraction)

Question: Subtract ( 4.567 ) from ( 15.123 ).

Solution:

Step 1: Write the numbers vertically, aligning decimal points.

( begin{array}{r} 15.123 \ -quad 4.567 \ hline end{array} )

Step 2: Subtract the numbers from right to left, borrowing where needed.

( begin{array}{r} 15.123 \ -quad 4.567 \ hline 10.556 end{array} )

Answer: ( 10.556 )

Example 2 (Subtraction)

Question: Subtract ( 2.8 ) from ( 7.05 ).

Solution:

Step 1: Write the numbers vertically, aligning decimal points and adding zeros.

( begin{array}{r} 7.050 \ -quad 2.800 \ hline end{array} )

Step 2: Subtract the numbers from right to left, borrowing where needed.

( begin{array}{r} 7.050 \ -quad 2.800 \ hline 4.250 end{array} )

Answer: ( 4.250 )

Quantitative Reasoning with Decimals

Quantitative reasoning problems involve applying mathematical skills to solve real-world situations. For decimals, these often involve money, measurements, or other quantities.

Example (Quantitative Reasoning)

Question: A tailor bought ( 2.75 ) metres of blue fabric and ( 3.5 ) metres of red fabric. How many metres of fabric did the tailor buy in total?

Solution:

Step 1: Identify the operation needed (addition).

Step 2: Write the numbers vertically, aligning decimal points and adding zeros.

( begin{array}{r} 2.75 \ +quad 3.50 \ hline end{array} )

Step 3: Add the numbers.

( begin{array}{r} 2.75 \ +quad 3.50 \ hline 6.25 end{array} )

Answer: The tailor bought ( 6.25 ) metres of fabric in total.

Checking Method

To check your answer for addition, you can subtract one of the numbers from the sum to see if you get the other number. For subtraction, you can add the difference to the number being subtracted to see if you get the original number.

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Activating prior knowledge

Teacher’s Activity: The teacher greets the pupils and asks them to recall what decimals are and where they see decimals in everyday life (e.g., money, measuring height). The teacher then introduces the topic of adding and subtracting decimals.

Pupils’ Activity: Pupils respond to questions about decimals and listen attentively to the introduction.

Learning Point: Decimal place value recall

Step 2: Introduction to Decimal Addition

Time: 7 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher explains the rules for adding decimals, emphasizing the alignment of decimal points. Using a chart, the teacher demonstrates step-by-step how to add two decimal numbers up to three decimal places, including adding zeros where necessary.

Pupils’ Activity: Pupils observe the demonstration, ask questions, and follow along with the steps.

Learning Point: Decimal addition rules

Step 3: Guided Practice – Decimal Addition

Time: 7 minutes

Teaching Skill: Guided Practice

Teacher’s Activity: The teacher writes a few addition problems on the board (e.g., ( 5.12 + 3.456 ), ( 0.789 + 1.2 )). Pupils are guided to solve them on their whiteboards or in their notebooks, with the teacher providing support and correcting errors.

Pupils’ Activity: Pupils attempt to solve the addition problems with teacher guidance.

Learning Point: Adding decimals accurately

Step 4: Introduction to Decimal Subtraction

Time: 7 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher explains the rules for subtracting decimals, again stressing decimal point alignment and the need to add zeros. Using another chart, the teacher demonstrates step-by-step how to subtract decimal numbers up to three decimal places, including borrowing.

Pupils’ Activity: Pupils observe the demonstration, ask questions, and follow along with the steps.

Learning Point: Decimal subtraction rules

Step 5: Guided Practice – Decimal Subtraction

Time: 7 minutes

Teaching Skill: Guided Practice

Teacher’s Activity: The teacher writes a few subtraction problems on the board (e.g., ( 9.876 – 2.12 ), ( 10.5 – 4.321 )). Pupils are guided to solve them, with the teacher offering assistance and checking their work.

Pupils’ Activity: Pupils attempt to solve the subtraction problems with teacher guidance.

Learning Point: Subtracting decimals accurately

Step 6: Quantitative Reasoning & Game

Time: 5 minutes

Teaching Skill: Problem Solving/Activity

Teacher’s Activity: The teacher presents a simple quantitative reasoning word problem involving decimal addition or subtraction. After solving it as a class, the teacher organises a short decimal number game (e.g., flash card challenge or a quick board game) where pupils practice adding and subtracting decimals in pairs or small groups.

Pupils’ Activity: Pupils participate in solving the word problem and actively engage in the decimal game.

Learning Point: Solving decimal word 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:

1. Add ( 4.25 + 7.893 ).
2. Subtract ( 6.125 ) from ( 10.000 ).
3. What is the first step when adding or subtracting decimals?
4. A rope is ( 8.5 ) metres long. If ( 2.75 ) metres are cut off, how much rope is left?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Decimal operations understanding

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 decimals 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 recaps the main points of the lesson, reinforcing the importance of aligning decimal points and checking answers. The teacher encourages pupils to practice more at home.

Pupils’ Activity: Pupils listen and ask any final questions.

Learning Point: Decimal operations consolidation

Continuous Assessment/Further Study

Type: Homework

Instruction: Solve the following problems in your mathematics notebook:

1. Add: ( 15.36 + 8.924 )
2. Subtract: ( 20.00 – 12.753 )
3. Find the sum of ( 0.45 ) and ( 3.128 ).
4. What is the difference between ( 9.6 ) and ( 5.38 )?
5. A bag of rice weighs ( 5.5 ) kg. Another bag weighs ( 3.25 ) kg. What is their total weight?

Lesson Keywords

• Decimal – A number that contains a decimal point, representing a whole number and a fractional part.
• Decimal point – The dot used to separate the whole number part from the fractional part of a decimal number.
• Place value – The value of a digit based on its position in a number (e.g., tenths, hundredths, thousandths).
• Addition – The process of combining numbers to find their sum.
• Subtraction – The process of taking one number away from another to find the difference.

Differentiation

For weaker learners: Provide additional practice with simpler decimal problems (one or two decimal places) and use visual aids like place value charts. Offer one-on-one support during guided practice.
For faster learners: Challenge them with more complex word problems involving multiple decimal operations or decimals with more places. Encourage them to create their own decimal problems for others to solve.

Suggested Lesson Videos

For further understanding and visual examples, search on YouTube for: adding and subtracting decimals primary 4 nigeria

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure you have charts with clear examples of decimal addition and subtraction, number cards, and flash cards ready. Pay close attention to the correct alignment of decimal points during demonstrations, as this is a common area of error for pupils. Guide pupils through the examples step-by-step, allowing them to participate in each stage of the calculation. Encourage collaboration during the game activity to foster peer learning. Ensure pupils copy the Board Summary notes accurately during the note-taking stage. Check their understanding frequently through questions and observe their work during practice sessions. Provide immediate feedback and support to those struggling, and offer extension activities to those who grasp the concepts quickly.