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Set Visual Lab

Pick an expression and the regions light up. Drop the numbers in and the counting rule stops being a rule.

✓ Free for everyone · works on a projector

UAB

A ∪ B 20 of the 30 numbers

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Mode

Expression

A′ is everything outside A — including the part of the box outside both circles.

Set names

Four ways to use it in class

  1. Shade A ∪ B, then (A ∪ B)′. Ask what is left over — the answer is the part of the box outside both circles, which most pupils forget exists.
  2. Put (A ∪ B)′ and A′ ∩ B′ side by side. The shading is identical; that is De Morgan's law, seen before it is written.
  3. Switch to counting. Add |A| and |B| out loud, then count the union on the screen — the difference is exactly the overlap, counted twice.
  4. Rename the sets to something from your class (plays football, plays music) and run the same survey question with the numbers still underneath.