Primes, HCF and LCM is usually met around Secondary 1 — though schools sequence topics differently — and is covered in Odyssey Math Tuition’s online math course for that level, with recorded video lessons, a question bank, topical practice and a topical test. Most marks lost here come from execution errors rather than misunderstanding, which is why targeted practice works.
What primes, hcf and lcm actually asks of a student
This topic builds on prime factorisation: expressing a number as a product of primes, then using that form to find the highest common factor and the lowest common multiple of two or more numbers.
It looks like arithmetic and behaves like algebra. The index notation introduced here is the same notation that governs surds, logarithms and polynomial work later, so a student who is fluent in prime factorisation has a head start well beyond this chapter.
What the topic assumes you already have
Most difficulty in this topic is not caused by the topic itself. It is caused by something earlier that never became fluent. Check these first:
- Recognising primes up to at least fifty
- Confident division and multiplication
- Index notation for repeated factors
- Systematic working rather than trial and error
If any of these is shaky, repair it before going further. Working on new material while a prerequisite is unstable is how students spend hours and move nothing.
Where marks are actually lost
- Confusing HCF with LCM, particularly in worded problems
- Missing a prime factor by dividing carelessly
- Taking the highest index for HCF instead of the lowest
- Answering with the prime factorisation when a number was asked for
- Applying the wrong one to a context question about repeating events
Most of these are execution errors rather than gaps in understanding, which is encouraging: they respond to practice and to keeping a written record of the mistakes you personally repeat.
A revision approach that works
- Write the prime factorisation of both numbers in index form before doing anything else.
- Remember the rule as words: lowest indices for HCF, highest for LCM.
- Practise worded problems specifically — deciding which is needed is the examined skill.
- Check by dividing: the HCF must divide both numbers exactly.
How the Secondary 1 course covers it
In the Secondary 1 online course this topic follows the same shape as every other: a recorded explanation, a question bank with answers worked through rather than printed, topical practice, and a topical test. Lessons are recorded personally by our founder, Mr. Justin Tan, and the course follows our own curriculum, aligned to the MOE syllabus.
The courses also include past-year school examination papers with worked answers, which shows how a topic is actually examined rather than how it is taught. Access is 24 hours a day with unlimited replays, and every online course carries a 7-day money-back guarantee.
Where this sits in the wider syllabus
For the year as a whole, see our guide to this stage. For the subject in context, this guide and this one cover what comes before and after.
Syllabus details follow Ministry of Education and SEAB published documents. Course details and prices are as published at the time of writing — check the course pages for current information. We do not promise grades.
Read next
Related reading on studying maths online: Inside the Secondary 1 Online Math Course, Basic Algebra and Algebraic Manipulation: A Secondary 1 Guide, Ratio, Rate and Speed: A Secondary 1 Revision Guide, Surds and Indices: A Secondary 3 A-Math Revision Guide, Matrices: A Secondary 4 E-Math Guide. On choosing a school at this stage, see our list of secondary schools in Singapore.
Frequently asked questions
What does primes, hcf and lcm cover at Secondary 1?
This topic builds on prime factorisation: expressing a number as a product of primes, then using that form to find the highest common factor and the lowest common multiple of two or more numbers.…
What should my child revise before this topic?
The prerequisites listed above. Most difficulty traces back to an earlier skill that never became fluent rather than to the topic itself.
Where do students lose the most marks?
Almost always in execution rather than understanding — sign errors, answering a different question from the one asked, or skipping the sketch.
Is this topic in the online course?
Yes. It is covered in the Secondary 1 online math course with video lessons, a question bank, topical practice and a topical test.
Can we access just this topic?
Yes. The courses are self-paced and non-linear, so a student can go straight to one topic without working through the rest.
Is there a trial period?
All online courses carry a 7-day money-back guarantee. The terms and conditions set out how it works.
Last reviewed July 2026. Syllabus details follow the Ministry of Education and SEAB published documents.
