You will learn
- Write money with two decimal places.
- Read measures in decimals.
- Add and subtract money and lengths.
- Convert between units using decimals.
Version 0.2 · expanded edition · expert review pending Standards alignment: pending verification. Written in the style of common primary school assessments. No exam result is promised.
Student lesson
- Money uses two decimal places.
- Line up the decimal points to add and subtract.
- Metres, kilograms and litres can be decimals.
- Convert units: 1 m = 100 cm, 1 kg = 1,000 g.
Words to know
A number with a point.
1/100 of a naira.
A unit of length.
A unit of mass.
1. Discover: at the shop
A book costs ₦3.75 and a pen ₦1.50. How much altogether? How many centimetres is 2.5 m?
2. Understand: decimals in real life
- 3.75 + 1.50 = 5.25 naira.
- 10.00 − 6.45 = 3.55.
- 2.5 m = 2.5 × 100 = 250 cm.
- 1.75 kg = 1.75 × 1,000 = 1,750 g.
Line up the decimal points when adding or subtracting.
Idea 1: Money
2.40 + 3.65: line up the points. The sum is 6.05. 10.00 − 6.45 = 3.55.
Idea 2: Length and mass
1.5 m = 1.5 × 100 = 150 cm. 0.5 kg = 0.5 × 1,000 = 500 g.
Idea 3: Adding decimals
4.2 + 3.85: write 4.20 + 3.85 = 8.05.
Why line up the points? Ones go under ones, tenths under tenths.
3. Worked examples
Example 1 (I show you): Add
2.40 + 3.65
- Line up the points.
Answer: 6.05
Example 2 (We do it together): Convert
1.5 m in cm
- 1 m = 100 cm.
Answer: 150 cm
Example 3 (You try): Convert
0.5 kg in g
Show the steps and answer
- 1 kg = 1,000 g.
Answer: 500 g
Did you know?
Kobo are hundredths of a naira, just like cents are hundredths of a dollar.
Why this matters
Decimals appear in prices, rulers and scales every day.
4. Explore: shop it
You need paper.
- Add 3.75 and 1.50.
- Subtract from 10.00.
- Convert 2.5 m to cm.
- Convert 1.75 kg to g.
Think about it: what did you notice?
5.25; 4.75; 250; 1,750.
5. Practise
Say it in a sentence
Use these starters when you talk about the lesson. Say them out loud.
- I line up the ___.
- The sum is ___.
- 1 m = ___ cm, so ___ m = ___ cm.
- The change is ___.
Guided practice
Question 1. 3.75 + 1.50?
5.25.
Question 2. 2.5 m in cm?
250 cm.
Question 3. 1.75 kg in g?
1,750 g.
Independent practice
Level 1: Start
- 2.40 + 3.65
- 10.00 − 6.45
- 1.5 m in cm
- 0.5 kg in g
- 4.2 + 3.85
Level 2: Grow
- 5.60 + 2.45
- 20.00 − 13.40
- 2.3 m in cm
Level 3: Stretch
- 7.85 + 12.40
- 1.75 kg in g
- Ben says 3.5 + 2.25 = 5.30. What is wrong?
Answers are in the answer key below. Try first, then check.
6. Apply: everyday mathematics
Ade buys items costing 3.75 and 1.50. He pays 10. What is his change?
Show a sample answer
4.75.
Another one. Ife buys rice for 6.50 and oil for 3.85 and pays 20.00. How much change?
Show a sample answer
6.50 + 3.85 = 10.35 and 20.00 − 10.35 = 9.65.
7. Common mistakes
Fix: Align the points.
Fix: Write the points in a column.
Fix: Write 3.5 as 3.50.
8. Lesson summary and revision card
- I can write money with two decimal places.
- I can read measures in decimals.
- I can add and subtract money and lengths.
- I can convert units using decimals.
9. Check and master
Answer all 14 questions. You will see feedback after each one.
Your result appears here after you answer every question.
10. Key takeaways
- Align decimal points.
- Money: two places.
- Multiply to change units.
11. Next lesson
Next lesson: Points. Keep going with the next idea in this course.
Exam practice
These questions are written in the style of common school and international primary assessments. Try them on your own, without looking back. Then check your answers in the marking guide. The marks are shown in brackets.
- Find 2.40 + 3.65. [2 marks]
- Find 10.00 − 6.45. [2 marks]
- Change 1.5 m to cm. [2 marks]
- Change 0.5 kg to g. [2 marks]
- Ali says 4.2 + 3.85 = 4.87. Is he right? Explain. [3 marks]
Total: 11 marks.
Marking guide and model answers
- Line up the points [1]; 6.05 [1]
- Line up the points [1]; 3.55 [1]
- 1 m = 100 cm [1]; 150 cm [1]
- 1 kg = 1,000 g [1]; 500 g [1]
- No [1]. Line up the points: 4.20 + 3.85 [1]. The sum is 8.05 [1].
Score guide: 10 to 11 = secure. 7 to 9 = nearly there, revise the parts you missed. Under 7 = work through the lesson again with a grown-up.
Printable worksheet
- 2.40 + 3.65
- 10.00 − 6.45
- 1.5 m in cm
- 0.5 kg in g
- 4.2 + 3.85
- 3.75 + 1.50 =
- 10.00 − 6.45 =
- 2.5 m =
- 0.5 kg =
- 4.2 + 3.85 =
Homework
Make a shopping list with prices and total them.
Answer key and marking scheme
| Question | Expected response | Marks |
|---|---|---|
| 2.40 + 3.65 | 6.05 | 2 |
| 10.00 − 6.45 | 3.55 | 2 |
| 1.5 m in cm | 150 | 2 |
| 0.5 kg in g | 500 | 2 |
| 4.2 + 3.85 | 8.05 | 2 |
| Total | 10 |
Practice answers: Worksheet: 1 6.05; 2 3.55; 3 150; 4 500; 5 8.05.
Quiz answers: 1 A, 2 B, 3 C, 4 A, 5 B, 6 A, 7 B, 8 C, 9 A, 10 B, 11 C, 12 A, Challenge 1 C, Challenge 2 C.
Extra worksheet answers (items 6 onward): 6 5.25; 7 3.55; 8 250 cm; 9 500 g; 10 8.05.
Independent practice answers. Level 1: 1 6.05; 2 3.55; 3 150 cm; 4 500 g; 5 8.05. Level 2: 1 8.05; 2 6.60; 3 230 cm. Level 3: 1 20.25; 2 1,750 g; 3 3.5 = 3.50, so 3.50 + 2.25 = 5.75..
Mastery and remediation
| Objective | Bronze (Developing) | Silver (Proficient) | Gold (Advanced) |
|---|---|---|---|
| O1 Write money with two decimal places | Shows this with help from an adult or a picture | Does this independently and explains how they know | Explains it clearly and uses it in a new situation |
| O2 Read measures in decimals | Shows this with help from an adult or a picture | Does this independently and explains how they know | Explains it clearly and uses it in a new situation |
| O3 Add and subtract money and lengths | Shows this with help from an adult or a picture | Does this independently and explains how they know | Explains it clearly and uses it in a new situation |
| O4 Convert between units using decimals | Shows this with help from an adult or a picture | Does this independently and explains how they know | Explains it clearly and uses it in a new situation |
Proposed Courseversity thresholds for this page: Bronze = at least 8 of 12 core questions correct; Silver = all 12; Gold = all 12 plus both challenge questions. A badge is never a full record of progress.
If a learner struggles
- Find the misconception: Not lining up the decimal points. Align the points.
- Explain another way: use real objects first, then pictures.
- Show a simpler example: Practise adding money.
- Guided practice: work through one example together and let the learner try the next one.
- Reassess: use the quiz again or the worksheet.
- Move on when the learner shows Silver-level evidence independently.
For parents and guardians
In this lesson your child uses decimals for money and measures. You do not need to be good at mathematics to help.
- Add up a shopping receipt together.
- Ask: are the points lined up?
- Measure with a ruler in metres and centimetres.
- Ask “how do you know?” after each answer, and listen.
- Praise effort, not only right answers. Mistakes are how we learn.
- Ten to fifteen minutes a day is better than one long session.
Teacher package
1–5. Objectives, prerequisites, materials, preparation, duration
Lesson objectives. Learners will: write money with two decimal places; read measures in decimals; add and subtract money and lengths; convert between units using decimals.
Prerequisite knowledge. Lessons 1 to 7.
Materials. Counters (stones, seeds or bottle tops), paper, pencils, board or chalkboard. Low-resource options: use stones, seeds, sticks, bottle tops or drawings in the sand or on the board instead of printed materials.
Preparation. Gather the counters and draw the example pictures on the board before the lesson.
Suggested duration. 45–60 minutes. It can be split into two shorter sessions.
6–9. Teaching procedure, explanation notes, guided and independent activities
Introduction (5 min). Start with the Discover situation and let learners suggest ideas before you teach.
Explanation (10 min). Teach the Understand section with real objects first, then pictures, then symbols and words.
Guided activity (10 min). You need paper. Learners follow the Explore steps in pairs.
Independent activity (10 min). Learners complete the independent practice and the worksheet.
Assessment and reflection (5 min). Ask each learner to say one thing they learned and how they know it.
Key questions. Are the points lined up? What unit are we using?
Teacher explanation notes. Use the concrete, pictorial, abstract order: real objects first, then pictures, then symbols and words. Return to real objects whenever a learner needs support.
10–12. Differentiation, formative assessment, common misconceptions
Support. Use real objects and work with a partner; say each step aloud together. Extension. Ask learners to make up their own example and explain it to a partner.
Formative assessment. Listen to learner explanations, ask “how do you know?”, and check the independent work.
Misconceptions. Not lining up the decimal points. Align the points.
13–15. Assessment questions, answer keys, marking scheme
Use the quiz and worksheet on this page. The 11-mark exam practice scheme, the 10-mark scheme and all answers are in the answer sections above. Re-check every answer and the marking scheme before publication.
16–19. Remediation, enrichment, homework, teacher reflection
Remediation. Practise adding money. Enrichment. Invite learners to find or create three more examples at home or in the classroom and explain them. Homework. See above.
Teacher reflection. After teaching, record: which concepts learners understood; which misconceptions occurred; which activities worked; which learners need more practice; and what to improve next time.
Sources and standards
Alignment is pending verification and no external endorsement is claimed. Reference starting points named in the Courseversity standard: Common Core State Standards for Mathematics, Cambridge Primary and the IB Primary Years Programme. Specific standard codes will be added once checked against the official documents.
Research used to shape this lesson. Common Core 4.MD.A.2 and 5.NBT.B.7; Cambridge Primary Mathematics Stage 4 and 5 (decimals in context). These sources informed the lesson; no official alignment is claimed.