Author note — to cover

Show by counting outcomes why adding double-counts events in both, then subtract the overlap to correct the total, supported by small Venn sketches. Keep it numerical: quoting the general addition law as a formula in union and intersection notation belongs at A level. Both tiers. Full Venn technique lives on the Diagrams topic. (P4, P6)

• Fluency — direct questions on events that overlap, limited to this lesson's stated scope (4 questions).
• Application — use the same skill in unfamiliar or contextual questions without introducing a later method (4 questions).
• Check — questions built around the exclusions and likely misconceptions named in the lesson brief (4 questions).