Probability of Combined Events is usually met around Secondary 4 E-Math — 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 probability of combined events actually asks of a student
Secondary 4 probability moves from single events to combined ones: two or more things happening, in sequence or together. Tree diagrams and possibility diagrams are the standard tools.
The distinction that governs everything is whether the events are independent. If the first outcome changes the probabilities for the second — drawing without replacement, for instance — the second set of branches must change accordingly, and this is where most marks are lost.
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:
- Single-event probability and the complement rule
- Fraction multiplication and addition
- Systematic listing without omissions
- Careful reading for “with” or “without replacement”
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
- Using the same probabilities on the second set of branches when there was no replacement
- Adding probabilities along a branch instead of multiplying
- Multiplying across separate outcomes instead of adding them
- Missing one of the paths that satisfies the condition
- Giving a probability greater than one without noticing
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
- Draw the tree for every question, with probabilities on each branch.
- Underline “with” or “without replacement” before drawing anything.
- Remember: multiply along a path, add between paths.
- Check that the probabilities on each set of branches sum to one.
How the Secondary 4 E-Math course covers it
In the Secondary 4 E-Math 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: Statistics and Data Analysis: A Sec 4 E-Math Guide, Plane Geometry: A Sec 4 A-Math Guide, Mensuration in Secondary 4 E-Math: A Revision Guide, Self-Paced Math Learning: Who It Suits, and Who It Does Not, Permutations and Combinations in H2 Mathematics: A JC2 Guide. On choosing a school at this stage, see our list of secondary schools in Singapore.
Frequently asked questions
What does probability of combined events cover at Secondary 4 E-Math?
Secondary 4 probability moves from single events to combined ones: two or more things happening, in sequence or together. Tree diagrams and possibility diagrams are the standard tools.…
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 4 E-Math 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.
