Probability
Events, probability, conditional probability, independence and tree diagrams for IB Applications and Interpretation SL, with worked IB exam questions.
Probability measures how likely an event is, with a number between and . In the IB almost everything comes down to four tools: describing events with sets and Venn diagrams, calculating probabilities with outcome tables and contingency tables, using conditional probability (and deciding whether two events are independent), and organising multi-stage experiments with tree diagrams. Exam questions often mix them in a single context problem, so the essential thing is knowing what to draw and which formula each phrase of the question asks for.
Recommended order
Follow the sections in order: events and sample space, probability and its properties, conditional probability and independence and finally compound experiments and tree diagrams. At the end you have the IB exam questions grouped by type.
Sets and Venn diagrams (topic 1) and fractions and percentages.
Sections in this topic
Sample space and events: union, intersection and Venn diagrams
Random experiments, the sample space and events, and how to combine them (union, intersection, complement) with Venn diagrams and tables. IB Applications SL.
3 worked examples Section 2Probability and its properties: Laplace, complement and union
What probability is, Laplace's rule, the axioms and the complement and union properties, with Venn diagrams and contingency tables. IB Applications SL.
3 worked examples Section 3Conditional probability and independence of events
How to calculate P(A|B), use the product rule, test independence and avoid confusing it with mutually exclusive events. IB Applications SL.
3 worked examples Section 4Compound experiments and tree diagrams
Building tree diagrams: multiply along branches, add paths for total probability, read conditional probability, with and without replacement. IB SL.
3 worked examples End of topicIB exam questions for topic 10
IB exam questions on probability: events, Venn diagrams, tables, conditional probability and tree diagrams, by type and level, with step-by-step solutions.
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