IB Maths AA SL 4.11 - Conditional Probability and Independence

This IB Maths AA SL Topic 4.11 – Conditional Probability and Independence resource develops students’ understanding of conditional probability and how restricting the sample space affects probability calculations. It begins by introducing the meaning of “given” and explaining that, in P(A|B), event B becomes the new sample space. Students learn to use the formal formula P(A|B) = P(A and B)/P(B) and rearrange it to calculate intersections using P(A and B) = P(B) × P(A|B).

The lesson then develops confidence in recognising and testing independent events. Students compare P(A|B) with P(A) and use the alternative condition P(A and B) = P(A) × P(B), while distinguishing independence from mutually exclusive events. Practice includes Venn diagrams, cards, probability statements, two-way tables, survey data, and medical contexts, with emphasis on interpreting results clearly and avoiding common exam errors. With clear definitions, worked examples, contextual applications, exam checklists, and fully worked solutions, this resource helps SL students build strong conditional probability reasoning in line with IB Mathematics AA expectations.