Cambridge IGCSE Mathematics · Syllabus 0580 · Probability
Introduction to Probability
What is Introduction to Probability?
Probability is a number from 0 to 1 that measures how likely an event is, where 0 means the event is impossible, 1 means it is certain, and values nearer 1 mean greater likelihood. In the Extended route the probability of event A is written P(A) and the probability that A does not occur is written P(A prime); probability notation is not required in the Core route, where the same ideas are stated in words. When every possible outcome is equally likely, P(A) is the number of favourable outcomes divided by the total number of possible outcomes, and the result may be given as a fraction, a decimal or a percentage, with fractional answers simplified. Because an event either occurs or does not occur, the two probabilities total 1, giving the complement rule that the probability an event does not occur is 1 minus the probability that it does, written P(A prime) equals 1 minus P(A) in the Extended route. The outcome information needed may come from a systematic list, a two-way table, a graph such as a bar chart, or a Venn diagram, which is limited to two sets in the Core route, and the counting method is valid only when the listed outcomes are genuinely equally likely.
This definition is part of the Probability chapter in Cambridge IGCSE Mathematics.