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Re: Toughest Probability Question

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pete wrote:
> 
> Seebs wrote:
> >
> > On 2011-12-13, pete <pfiland@mindspring.com> wrote:
> > > divya bisht wrote:
> > >> How many people must be gathered together in a room,
> > >> before you can be
> > >> certain that there is a greater than 50/50 chance
> > >> that at least two of
> > >> them have the same birthday?
> >
> > >> Discuss Solution in link below
> >
> > > The probability that 23 random birthdays are all different is 0.492703
> >
> > So?
> 
> I made a mistake in the program.

I had it right the first time, 
but I rewrote the whole thing anyway.

/* BEGIN output from new.c */

The probability that out of 23 random birthdays,
that at least two are the same is 0.507297

/* END output from new.c */


/* BEGIN new.c */

#include <stdio.h>

#define YEAR                365  /* 366 */
#define PROB_SOME_SAME      0.5
#define PROB_ALL_DIFFERENT  (1 - PROB_SOME_SAME)

int 
main(void)
{
    int days = YEAR;
    double probability = 1;
    int people = 1;
    puts("\n/* BEGIN output from new.c */\n");
    do {
        ++people;
        --days;
        probability *= 1.0 * days / YEAR;
    } while(probability > PROB_ALL_DIFFERENT);
    printf("The probability that out of %d "
        "random birthdays,\n"
        "that at least two are the same is %f\n", 
        people, 1 - probability);
    puts("\n/* END output from new.c */");
    return 0;
}

/* END new.c */


-- 
pete

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Re: Toughest Probability Question pete <pfiland@mindspring.com> - 2011-12-12 19:29 -0500
  Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-13 04:46 +0000
    Re: Toughest Probability Question Geoff <geoff@invalid.invalid> - 2011-12-12 22:19 -0800
      Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-13 09:19 +0000
        Re: Toughest Probability Question "BartC" <bc@freeuk.com> - 2011-12-13 13:43 +0000
          Re: Toughest Probability Question Keith Thompson <kst-u@mib.org> - 2011-12-13 10:27 -0800
            Re: Toughest Probability Question "BartC" <bc@freeuk.com> - 2011-12-13 19:52 +0000
              Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-13 20:06 +0000
              Re: Toughest Probability Question Keith Thompson <kst-u@mib.org> - 2011-12-13 12:14 -0800
                Re: Toughest Probability Question "BartC" <bc@freeuk.com> - 2011-12-13 23:34 +0000
                Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-14 00:24 +0000
          Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-13 19:27 +0000
            Re: Toughest Probability Question "BartC" <bc@freeuk.com> - 2011-12-13 23:56 +0000
              Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-14 00:24 +0000
                Re: Toughest Probability Question "BartC" <bc@freeuk.com> - 2011-12-14 12:12 +0000
                Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-14 17:47 +0000
                Re: Toughest Probability Question gordonb.qunma@burditt.org (Gordon Burditt) - 2011-12-15 08:22 -0600
                Re: Toughest Probability Question Robert Wessel <robertwessel2@yahoo.com> - 2011-12-15 14:41 -0600
                Re: Toughest Probability Question superpollo <superpollo@tznvy.pbz> - 2011-12-15 19:14 +0100
                Re: Toughest Probability Question Keith Thompson <kst-u@mib.org> - 2011-12-14 13:12 -0800
                Re: Toughest Probability Question Willem <willem@toad.stack.nl> - 2011-12-14 21:53 +0000
                Re: Toughest Probability Question "BartC" <bc@freeuk.com> - 2011-12-14 22:35 +0000
                Re: Toughest Probability Question Willem <willem@toad.stack.nl> - 2011-12-15 09:07 +0000
                Re: Toughest Probability Question Geoff <geoff@invalid.invalid> - 2011-12-15 02:07 -0800
                Re: Toughest Probability Question Keith Thompson <kst-u@mib.org> - 2011-12-15 12:13 -0800
                Re: Toughest Probability Question Geoff <geoff@invalid.invalid> - 2011-12-15 13:03 -0800
                Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-15 21:36 +0000
              Re: Toughest Probability Question Geoff <geoff@invalid.invalid> - 2011-12-13 16:35 -0800
                Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-14 01:20 +0000
              Re: Toughest Probability Question Keith Thompson <kst-u@mib.org> - 2011-12-13 16:44 -0800
                Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-14 01:20 +0000
                Re: Toughest Probability Question James Dow Allen <jdallen2000@yahoo.com> - 2011-12-15 02:33 -0800
                Re: Toughest Probability Question gwowen <gwowen@gmail.com> - 2011-12-15 05:38 -0800
                Re: Toughest Probability Question Thad Smith <ThadSmith@acm.org> - 2011-12-18 23:34 -0700
                Re: Toughest Probability Question Bill Reid <hormelfree@gmail.com> - 2011-12-14 07:07 -0800
    Re: Toughest Probability Question Kaz Kylheku <kaz@kylheku.com> - 2011-12-13 06:55 +0000
      Re: Toughest Probability Question Seebs <usenet-nospam@seebs.net> - 2011-12-13 09:19 +0000
    Re: Toughest Probability Question pete <pfiland@mindspring.com> - 2011-12-13 12:15 -0500
      Re: Toughest Probability Question pete <pfiland@mindspring.com> - 2011-12-13 13:20 -0500
        Re: Toughest Probability Question Peter Nilsson <airia@acay.com.au> - 2011-12-13 18:15 -0800
          Re: Toughest Probability Question pete <pfiland@mindspring.com> - 2011-12-13 21:52 -0500

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