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Expected outcomes use probability to predict how many times an event should occur over a number of trials. Students multiply probability by the number of trials and compare expected results with experimental data.
Students make these errors again and again. Knowing them in advance gives you a head start.
Expecting experimental results to match theoretical probability exactly
Confusing expected frequency with actual frequency
Forgetting that expected outcomes can be non-whole numbers
Insights pulled from Cambridge IGCSE (0580) examiner reports — the exact mistakes candidates make every year.
In probability without replacement, the denominator DECREASES by 1 for each subsequent pick (13 → 12 → 11...). Getting 104/169 instead of the correct answer usually means you forgot this.
Source: CIE 0580 · Feb/March 2024 · Paper 2 · Q25
For 'exactly one green button' out of two picks, there are TWO orderings: green-then-not OR not-then-green. Calculate one product and DOUBLE it (or add both products).
Source: CIE 0580 · May/June 2023 · Paper 4 · Q15
In a histogram, bar HEIGHT = frequency density (frequency ÷ class width). Find the scale using a bar whose frequency AND width you know, then apply it to the others.
Source: CIE 0580 · Feb/March 2022 · Paper 4 · Q5b
Based on 3of 500+ insights extracted from CIE 0580 examiner reports (2018–2024).
This topic appears in the Cambridge IGCSE past papers. Our AI tutor can help with it on any question.
Useful for this topic:
Basic probability introduces the scale from 0 to 1 and the idea of equally likely outcomes. Students calculate probabilities of single events, understand mutually exclusive events, and work with the probability that something does not happen.
Combined events involve finding the probability of two or more things happening together or in sequence. Students use the addition rule for OR and the multiplication rule for AND, applying these to independent and dependent events.
Sampling methods determine how data is collected for a statistical investigation. Students must understand random, systematic and stratified sampling, and evaluate the strengths and limitations of each method.
Take our free diagnostic quiz to find out exactly where you stand, then practise probability with our AI tutor.
Probability trees, Venn diagrams, and data guides