Ed Gain
Member
Registered: Mar 2000
Location: San Diego, CA USA
Posts: 89 |
 Status
Yes Parb33, you are correct. The odds of Mirandu2000 and any 'selected' person having the same birthday are 1 in 365. But the odds of any two people in a crowd of 30 people having the same birthday is about 70%
Here is how it works...
Ignoring the minor technicality of leap years, it's clear that in a group of 366 people, at least two must share a birthday. Yet it seems counterintuitive to many that only 23 people are needed in a group to have a 50-50 chance of at least one coincidental birthday.
To see why it takes just 23 people to reach even odds on sharing a birthday, you have to look at the probabilities. Assume that all 365 days have an equal chance of being a birthday. For a party of one, there is no possibility of a coincidence. So, the probability of that particular date being a unique birthday is 365/365. For a second person to have a birthday that doesn't match that of the first, he or she must be born on any one of the other 364 days of the year.
You obtain the probability of no match between the birthdays of two people by multiplying 365/365 times 364/365, which equals .9973. Hence, the probability of a match is 1 - .9973, or .0027, which is much less than 1 percent.
With two people, there are 363 unused birthdays. The probability that a third person has a birthday that differs from the other two distinct birthdays is 363/365. So, for three people, the chance of having no pair of matching birthdays is 365/365 x 364/365 x 363/365, or .9918.
As the number of people brought into the group increases, the chance of there being no match decreases. By the time the crowd numbers 23 people, the probability of no matching birthdays is .4927. Thus, the chance of at least one match within a group of 23 people is .5073, or slightly better than 50 percent.
The reason the number is as low as 23 is that you aren't looking for a specific match. It doesn't have to be two particular people or a given date. Any match involving any date or any two people is enough to create a coincidence. Indeed, there are 253 different pairings possible among 23 people, any of which could lead to a match.
VTL - I grew up on the Beetles, Peter, Paul and Mary and Janis Joplin. If you are feeling old, then I must be ancient.
I remember seeing a quiz many years ago that would show you a picture and you would have to write down what the item was. At the end of the quiz you would compare your answers with a list of possible answers and score yourself accordingly. Your final score would be your approximate age. For instance one of the photos was of a refrigerator, but depending on if you called it an 'Ice Box', 'Fridge' or 'Refrigerator' you would get a different score. All this talk about age and 'artists' makes me wonder if you could devise a music quiz that could be used to determine a persons (approximate) age.
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03-16-2001 05:04 AM
I did the math
Nope
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