Probability · Venn diagrams & set notation
Chapter 1 · 3
The idea
Venn diagrams
Building a Venn diagram from worded information — why you fill the overlap first and work outwards, what the number in a region actually counts, the universal set and the "neither" region outside the circles, and how the grand total pins down whichever region is missing.
A full journey — read it, play with it, work it, then earn real exam marks. Everything stays on the timeline below.
In this lesson — start anywhere
Probability · Venn diagrams & set notation
Venn diagrams
Building a Venn diagram from worded information — why you fill the overlap first and work outwards, what the number in a region actually counts, the universal set and the "neither" region outside the circles, and how the grand total pins down whichever region is missing.
Why it works
A sorting machine
A Venn diagram is a sorting machine. You draw a rectangle for everybody in the survey — the universal set, labelled — and inside it a circle for each group. Every single person then lands in exactly one region of the picture: inside both circles, inside just one of them, or inside none at all. Nobody is left out and nobody appears twice. That "exactly one region each" property is the whole reason the diagram is trustworthy, and it is also the thing beginners break within about ten seconds.Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
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