Venn diagrams
Set notation: union (∪), intersection (∩), complement (′). Two and three-set diagrams.
Each circle represents a set. The intersection contains elements in both. Total inside the universal set adds to whatever the question states (count or probability).
Worked examples
A ∪ B = elements in either A or B (or both).
A ∩ B = elements in both A and B.
A′ = elements not in A.
Frequently asked questions
Filling in?
Always start with the intersection (the centre overlap), then work outwards using the totals.
Probability via Venn?
Each region's count divided by the total gives the probability of that region.