2.1StatisticsCore

Set Notation

Set notation gives a precise language for probability. Union, intersection and complement describe how events combine, and they map directly onto regions of a Venn diagram.

22 min Video by Zeeshan Zamurred Conditional Probability

Edexcel A level Maths: 2.1 Set NotationWatch the full walkthrough before the notes below.

Open on YouTube

What you'll be able to do

Use ∪, ∩ and complement notation
Translate between words and symbols
Relate notation to Venn diagram regions
Express probabilities using set notation

The symbols

$A \cup B$ is “ $A$ or $B$ ” (union). $A \cap B$ is “ $A$ and $B$ ” (intersection). $A^{'}$ is “not $A$ ” (complement). $P (A^{'}) = 1 - P (A)$ .

A \cup B (or), A \cap B (and), A^{'} (not)

Core set operations.

P (A^{'}) = 1 - P (A)

= 1 - 0.3 = 0.7

Answer

0.7

Tip — ∪ looks like a U for “Union/or”; ∩ is the cap for “and”.

Venn diagram regions

Each set expression shades a region: $A \cap B$ is the overlap, $A \cup B$ is everything in either circle, $A^{'}$ is everything outside $A$ .

Formula recap

A \cup B = A or B

Union.

A \cap B = A and B

Intersection.

P (A^{'}) = 1 - P (A)

Complement.

Common mistakes to avoid

Swapping ∪ and ∩.

∪ = or (union); ∩ = and (intersection).

Writing P(A′) = −P(A).

P(A′) = 1 − P(A).

Key takeaways

∪ = or, ∩ = and, A′ = not.
P(A′) = 1 − P(A).
Set expressions correspond to Venn diagram regions.

Test yourself

Ready to lock in Set Notation? Pick a mode and earn XP & Dobloons.