Re: Birthday Problem

From: Gary Labowitz (glabowitz_at_comcast.net)
Date: 04/13/04 

Date: Mon, 12 Apr 2004 22:50:54 -0400

"Sandra" <s.cantrell@mindspring.com> wrote in message
news:407b2637.5311140@news.east.earthlink.net...
> On Mon, 12 Apr 2004 23:21:26 GMT, alfps@start.no (Alf P. Steinbach)
> wrote:
>
>
> >
> >Well, it seems your work is cut out for you, unless the context of
the
> >problem formulation is such that it really means something more
than stated.
> >
> >All your program has to do is to ask you whether your birthday is
February
> >29th, and then apply the formula inconsiderately given you by
Robert
> >E. Tisdale and at least one more poster. The program could output
one
> >result based on the current year or on assuming a non leap-year, or
it could
> >output two result, one for non-leap and one for leap-year. In the
latter case
> >the formula should be suitably modified for leap year. Of course
it could
> >also output four results, one for each combination of February 29th
or not and
> >leap year or not. That way you could avoid the input part.
> >
> >Also, it might be possible to avoid the leap year thing by
analyzing whether
> >it can affect the result or not.
> >
> >--
> >A: Because it messes up the order in which people normally read
text.
> >Q: Why is top-posting such a bad thing?
> >A: Top-posting.
> >Q: What is the most annoying thing on usenet and in e-mail?
>
>
> Thanks Alf - I am working on an encyrption\decryption program right
> now so I think I am going to let this one go. I really am stuck :)
>
> He is going to give us the answer on Wed - Do you want to see what
he
> comes up with ?

You bet. Especially since you cannot know, without some distribution
information, how many people it will take to find your birthday.
If you were born on 1-1 and asked people as they got off the subway if
anyone was born on 1-1 there is no telling how many people you would
ask before one of them was born on 1-1. It's not the pigeon hole
principle here. You might go through 1,000,000 people until one was
born on 1-1. There is just no way of telling.
If, on the other hand, you were asking people what their birthdates
were and kept track of the answers, you might be surprised to find
that after the first 20 you will have a 50-50 chance of finding two of
them with the same birthday. But it is a different problem.

I think your teacher is on a wrong track. 

-- 
Gary (who was a math major, but not really very good at statistics)

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