# Couple has two children **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [February 27, 2009, 7:39am UTC](https://boards.straightdope.com/t/couple-has-two-children/487631 "2009-02-27T07:39:24Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [April 1, 2009, 3:47pm UTC](https://boards.straightdope.com/t/couple-has-two-children/487631/21 "2009-04-01T15:47:21Z")
> [@md2000](#): > > Similarly, if they say “one child is a girl, what are the odds the oldest is a boy?”. Now, the knowledge that one child is a girl is irrelevant to the scenarios. That may or may not be the oldest. So the odds are still 50-50? So if they say “one child is a boy, what are the odds the oldest is a boy?” - same odds? Ignoring semantical quibbles for a moment, the knowledge that one child is a girl is _not_ irrelevant to the scenarios. This knowledge eliminates the boy-boy scenario. Likewise, knowing that one child is a boy eliminates the girl-girl scenario. ---
**Author:** ![Blue\_Mood](https://avatars.discourse-cdn.com/v4/letter/b/ac91a4/32.png) [@Blue\_Mood](https://boards.straightdope.com/u/Blue_Mood)\ **Post date:** [April 1, 2009, 4:24pm UTC](https://boards.straightdope.com/t/couple-has-two-children/487631/22 "2009-04-01T16:24:59Z")
> [@md2000](#): > > Similarly, if they say “one child is a girl, what are the odds the oldest is a boy?”. Now, the knowledge that one child is a girl is irrelevant to the scenarios. That may or may not be the oldest. So the odds are still 50-50? So if they say “one child is a boy, what are the odds the oldest is a boy?” - same odds? > > Hmmm… If you know that \*exactly \*one child is a boy, then the options are as follows: 1. older child boy, younger child girl 2. older child girl, younger child boy So yes, the odds are one out of two, or 50-50, of the oldest being a boy. However, saying “one child is a boy” does not necessarily mean that only one child is a boy. In mathematics you have to be very exact and say something like “exactly one child is a boy” or “one and only one child is a boy”. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [April 1, 2009, 6:15pm UTC](https://boards.straightdope.com/t/couple-has-two-children/487631/23 "2009-04-01T18:15:22Z")
[QUOTE=Blue Mood] In mathematics you have to be very exact and say something like “exactly one child is a boy” or “one and only one child is a boy”. [/QUOTE] Yes, whereas in English if you say “one child is a boy” the default assumption is that the other child is not. 😉 ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [April 2, 2009, 2:07pm UTC](https://boards.straightdope.com/t/couple-has-two-children/487631/24 "2009-04-02T14:07:56Z")
> [@Irishman](#): > > Yes, whereas in English if you say “one child is a boy” the default assumption is that the other child is not. 😉 Sorry, yes, my semantics were out to lunch. :smack: “Exactly one child is a boy” - odds oldest is a boy is 50-50. (BG or GB) “At least one child is a boy” - odds oldest is a boy - 2 in 3 (BB, BG, GB). In the “Exactly…” case, the definition of “one is a boy” conveys no information that determines order. It does, however, eliminate the cases BB and GG so the odds are still 50-50. The “at least…” case is basically the original one, one child walks into a room… ---
**Author:** ![Frylock](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@Frylock](https://boards.straightdope.com/u/Frylock)\ **Post date:** [April 3, 2009, 1:37pm UTC](https://boards.straightdope.com/t/couple-has-two-children/487631/25 "2009-04-03T13:37:04Z")
A few people in this thread have said the boy/girl problem as usually stated (and as stated in Cecil’s column) is ambiguous. I disagree that it is ambiguous in any interesting way relevant to the puzzle, and I definitively explained exactly why it’s not ambiguous [here](http://boards.straightdope.com/sdmb/showpost.php?p=7678935&postcount=121). Unfortunately no one has ever acknowledged the definitiveness of my argument in that post. 🙂 But there it is. [Previous page](https://boards.straightdope.com/t/couple-has-two-children/487631.md?page=1)