Convert metric lengths, masses and time without mixing quantities
Choose a unit for the quantity being measured · Convert lengths and masses using a consistent factor · Convert hours and minutes using 60 rather than a metric prefix
Exam scope and assessment notes
Core and Extended foundations. Historical study of Cambridge IGCSE Mathematics (US) 0444, 2025 Version 2. The final assessment was June 2025; the syllabus was available only to schools in Arizona, USA. This is not a current exam-entry option. Original self-check teaching and explained practice are not Cambridge papers, official marks or predicted grades. Linked teaching foundations do not establish full syllabus mastery. Calibrated cumulative assessment, reliable drawn-work review and qualified mathematics-teacher review remain unfinished.
Before you begin
- Place value
- Time intervals
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What should you establish before applying the method in this lesson?
What you will learn
- Choose a unit for the quantity being measured
- Convert lengths and masses using a consistent factor
- Convert hours and minutes using 60 rather than a metric prefix
Match the quantity
For length, 10 mm = 1 cm, 100 cm = 1 m and 1000 m = 1 km. For mass, 1000 g = 1 kg. Multiply when converting to smaller units and divide when converting to larger ones. Write the units at each step so an intermediate factor can be checked.
A mass in grams cannot be converted to centimetres: those measure different quantities. A conversion changes the numerical description, not the physical amount.
Time has different factors
1 hour = 60 minutes and 1 minute = 60 seconds. Thus 1.5 hours is 90 minutes, not 150 minutes. For a mixed interval, convert each part before adding: 2 hours 15 minutes = 135 minutes. Use the time and calendar conventions stated in the question.
Sources for this lesson
Pause and explain
How many minutes are in 1.5 hours?
Worked example
Convert 2.35 m to centimetres and 0.8 kg to grams.
Show the worked solution
- 2.35×100 = 235 cm.
- 0.8×1000 = 800 g; the quantities remain length and mass.
Answer 235 cm; 800 g.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Convert 3.2 km to metres and 48 mm to centimetres.
Give me a hint
Use 1000 m per km and 10 mm per cm.
Compare my reasoning
- 3.2×1000 = 3200 m.
- 48÷10 = 4.8 cm.
3200 m; 4.8 cm.
Look for these in your work
- Choose the right factor
- State both units
Convert 2750 g to kilograms and 2 hours 15 minutes to minutes.
Give me a hint
Convert the parts separately.
Compare my reasoning
- 2750÷1000 = 2.75 kg.
- 2×60+15 = 135 minutes.
2.75 kg; 135 minutes.
Look for these in your work
- Preserve the quantity
- Use 60 for time
A ribbon is 1.2 m long. Three pieces, each 35 cm, are cut without wastage. Find the remaining length in centimetres.
Give me a hint
Put all lengths in the same unit first.
Compare my reasoning
- 1.2 m = 120 cm; the pieces total 105 cm.
- Remaining length = 120−105 = 15 cm.
15 cm.
Look for these in your work
- Convert before subtracting
- Check the result is feasible
Common mistakes
- A minute is not one hundredth of an hour.
- Keep the measured quantity unchanged.
What can you explain now?
How many minutes are in 1.5 hours?
Compare with the explanation
90 minutes.
Multiply hours by 60.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How many minutes are in 1.5 hours?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.