[BruceZ]

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I won't agree completely that this is the correct number. The calculation is fine, but the assumption of equally distributed birthdays is invalid (amusingly, this very topic was recently discussed in a recent issue of Amstat they print for students such as myself). Without thinking at all about the math, my first guess would be the chances are higher.

[/ QUOTE ]

The birthday problem is an old and famous problem, and it is generally assumed in the problem statement that there are 365 equally distributed birthdays. This case is all you need to realize the essential point that 25 people give you a huge advantage on an even-money bet.