In this three-door game-show puzzle, switching wins with probability 2/3 when an informed host always reveals a goat and offers a switch.

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Your new ahaThe Monty Hall Problem

The Monty Hall Problem: Counterintuitive puzzle involving switching doors. Source: Monty Hall problem ↗

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09This birthday-sharing puzzle reaches just over a 50% match probability with 23 people under the usual equal-day assumptions.RECALL
The Birthday Paradox
The birthday paradox shows that just 23 people give roughly even odds that two share a birthday.
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10In this statistical paradox, a trend in separate groups reverses when the groups are combined.RECALL
Simpson's Paradox
Simpson's paradox shows a data trend can reverse once separate groups are combined, a caution for statistics.
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11One sealed envelope contains twice the money in the other; this puzzle exposes faulty reasoning that seems to favour switching whichever one you chose.RECALL
The Two Envelopes Problem
The two envelopes problem seems to always favor switching, exposing a flaw in naive expected-value reasoning.
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