This page is maintained by
Thomas Bending,
and was last modified on 29 July 2011.
Comments, criticisms and suggestions are welcome.
Copyright © Thomas Bending 2012.
In a group of 23 people the chances are better than evens that two will share a birthday. Consider a variety of other random choices, such as thinking of a playing card, picking a lottery ticket, etc. Say that we have a match if there are two people that make the same choice.
Q: 1. How many people do we need for the probability of a match to be better than evens?
Q: 2. If we ask the birthdays (or whatever) of a sequence of people, what's the expected number until we find the first match?
[TB, 24 Jan 2002]
A:
| Probability | Question 1 | Question 2 | |
|---|---|---|---|
| 1 in | # people | # people (2dp) | |
| Cards in a pack | 52 | 9 | 9.72 |
| Birthdays | 365 | 23 | 24.62 |
| 1,000 | 38 | 40.30 | |
| 1,000,000 | 1178 | 1253.98 | |
| UK National Lottery tickets | 13,983,816 | 4404 | 4687.47 |
The last two involve Stirling approximations, but are probably correct as quoted.
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This page is maintained by
Thomas Bending,
and was last modified on 29 July 2011.
Comments, criticisms and suggestions are welcome.
Copyright © Thomas Bending 2012.