Probability
From "how likely" to tree diagrams, conditional probability and without-replacement, the reasoning the exam actually tests.
What this lesson covers
Probability is a 7-part O Level Mathematics lesson. Each part makes one point and then hands over to the next, so it can be read in a sitting or picked up again at the part you stopped on. It defines the idea in plain words before using it, works through an example step by step, breaks the topic into its parts and compares them, names the mistakes that cost marks in an exam, ends with a recap of what to remember.
How it begins
A probability is a number from 0 (impossible) to 1 (certain). For equally likely outcomes it is favourable outcomes ÷ total outcomes: one die, P(even) = 3/6. From data it is the relative frequency: 46 out of 200 trials gives 0.23, and the expected number in 20 more trials is 0.23 × 20. P(not A) = 1 − P(A). This is the most underused fact in the topic.
The 7 parts
- What a probability is
- Trees: multiply along, add across
- Without replacement
- Conditional probability
- Where marks go
- What to remember
- Watch one worked through
Practise Probability
Everything on QuizByt for O Level Mathematics that goes with this lesson: read it first, then test yourself while it is fresh.
🧠 5 quizzes on Probability (2 easy, 2 medium, 1 hard)
Work up from easy to hard: the hard quiz asks the O Level exam-style questions on Probability.
🖨️ Printable worksheet
Probability on paper for O Level, with room to write the working out. Preview the first page free.
🎮 Games for O Level Mathematics
Number and logic games at the right level for O Level. Passing a quiz on Probability earns the credits that open them.
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