What is the 'Birthday Problem' with 365 days?

Approach: Calculate the probability that no two people share a birthday.

The probability that in a set of n people, at least two will share a birthday. For n=23, the probability is approximately 50.7%. Calculated as 1 - (365! / (365^n * (365-n)!)).

Follow-up: Why is this number lower than most people expect?

Key concepts: complementary probability, counting.