Brain Teasers & Mental Math
The Birthday Problem: in a room of 23 people, what's roughly the probability that at least two share a birthday — and why is it surprisingly high?
Model answer
About 50% (≈ 50.7%).
Use the complement — probability everyone is distinct: (365/365)(364/365)(363/365)…(343/365) for 23 people. That product is ≈ 0.493, so P(a shared birthday) ≈ 1 − 0.493 ≈…
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