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What are the odds of a couple's second child being a boy?

Chizz
Chizz Posts: 28,329
edited January 2017 in Fun, Jokes & Captions
Here's the scenario:

You meet a couple. They tell you they have two children. One child is a boy. What is the probability that the other child is also a boy?
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Comments

  • shirty5
    shirty5 Posts: 19,212
    Burlington Bertie
  • se9addick
    se9addick Posts: 32,030
    Chizz said:

    Here's the scenario:

    You meet a couple. They tell you they have two children. Their oldest child is a boy. What is the probability that the second child is also a boy?

    I would assume, without any other information on the couple, it's 50/50 but I'm not sure if there's a medical reason for people being more likely to produce either boys or girls.
  • PaddyP17
    PaddyP17 Posts: 13,035
    Well, according to this chart, bang on 50/50.

    http://www.ingender.com/gender-info/odds-of-having-another-boy-or-girl.aspx

    "Odds of Having a Girl After 1, 2, or 3 Boys

    The odds of having a girl seem decrease after having each boy, but only very slightly. Even after 3 boys, you are only 6.4% more likely to have a 4th boy than a girl."
  • C_A_F_C
    C_A_F_C Posts: 3,866
    This is a joke?
  • 50/50.

    When I was little, I used to think boys came from one bollock and girls from the other. I was never very good at science.

  • Lincsaddick
    Lincsaddick Posts: 32,345
    I digress a bit .. BUT ... a good friend of my ex wife had given birth to five girls, she was really desperate to give her husband a son but was equally sick of being almost permanently pregnant .. she and her hubby ran a successful business and over the years made a nice few quid .. so .. if at first (or five times) you don't succeed, try again
    at the age of (about) 43 after a failure to conceive naturally, she paid for IVF treatment in a last attempt to birth a son ..
    IVF was so successful that she became pregnant with quads, no messing there, not twins, not triplets, 'kin quads .. birth time .. out they came .. number 1 .. a girl .. number 2 .... a girl ... number 3 ... a girl .. desperate times .. number 4 ? .. go on guess



    boy !!!! .. so eight girls and one lil boy ((:>) .. and she insisted it was all worth it .. one of those 'you could NOT make it up' stories
  • I digress a bit .. BUT ... a good friend of my ex wife had given birth to five girls, she was really desperate to give her husband a son but was equally sick of being almost permanently pregnant .. she and her hubby ran a successful business and over the years made a nice few quid .. so .. if at first (or five times) you don't succeed, try again
    at the age of (about) 43 after a failure to conceive naturally, she paid for IVF treatment in a last attempt to birth a son ..
    IVF was so successful that she became pregnant with quads, no messing there, not twins, not triplets, 'kin quads .. birth time .. out they came .. number 1 .. a girl .. number 2 .... a girl ... number 3 ... a girl .. desperate times .. number 4 ? .. go on guess



    boy !!!! .. so eight girls and one lil boy ((:>) .. and she insisted it was all worth it .. one of those 'you could NOT make it up' stories

    Should have just adopted!
  • Lincsaddick
    Lincsaddick Posts: 32,345

    I digress a bit .. BUT ... a good friend of my ex wife had given birth to five girls, she was really desperate to give her husband a son but was equally sick of being almost permanently pregnant .. she and her hubby ran a successful business and over the years made a nice few quid .. so .. if at first (or five times) you don't succeed, try again
    at the age of (about) 43 after a failure to conceive naturally, she paid for IVF treatment in a last attempt to birth a son ..
    IVF was so successful that she became pregnant with quads, no messing there, not twins, not triplets, 'kin quads .. birth time .. out they came .. number 1 .. a girl .. number 2 .... a girl ... number 3 ... a girl .. desperate times .. number 4 ? .. go on guess



    boy !!!! .. so eight girls and one lil boy ((:>) .. and she insisted it was all worth it .. one of those 'you could NOT make it up' stories

    Should have just adopted!

    not even a thought in her head about that ..

  • Chizz
    Chizz Posts: 28,329
    C_A_F_C said:
    That's interesting. But there's nothing on that page that provides an answer to the question.
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  • Chizz
    Chizz Posts: 28,329
    se9addick said:

    Chizz said:

    Here's the scenario:

    You meet a couple. They tell you they have two children. Their oldest child is a boy. What is the probability that the second child is also a boy?

    I would assume, without any other information on the couple, it's 50/50 but I'm not sure if there's a medical reason for people being more likely to produce either boys or girls.
    Yes, a lot of people would assume that. As did I until I heard the answer.
  • Chizz
    Chizz Posts: 28,329
    It's interesting to see that @shirty5 is by far the closest, so far.
  • Daddy_Pig
    Daddy_Pig Posts: 496
    Cant remember which way round it is but one sex sperm swims faster than the other but has a shorter life span.

    Therefore if the couple had "relations" at the time of ovulation it is likelier to have sex 1. The further back you go before ovulation increases the chances of the baby being sex 2.

    Science.
  • DaveMehmet
    DaveMehmet Posts: 21,587
    Daddy_Pig said:

    Cant remember which way round it is but one sex sperm swims faster than the other but has a shorter life span.

    Therefore if the couple had "relations" at the time of ovulation it is likelier to have sex 1. The further back you go before ovulation increases the chances of the baby being sex 2.

    Science.

    It must be the boy sperm that lives longer as I'm shit at swimming.
  • Probably total bollox so don't take it as gospel and Not clicking on the link so no idea what they say but, going by an 'old wives tale' if the first was a boy then I suspect the next one will also be a boy. Doesn't producing girls need something a little extra from the male donors sperm so, if that is the case, then if that something extra wasn't present when the first child was conceived then chances are it's not going to be there when producing subsequent children.
  • DRAddick
    DRAddick Posts: 3,588
    A relation of mine had a daughter as a first born who sadly past away shortly after birth. She went on to have a son next but was also desperate to have another girl. Gave up after 4 boys, all single births.
  • Leuth
    Leuth Posts: 23,312
    If they had two boys they'd have said 'two boys' not two children. 100% a girl
  • SELR_addicks
    SELR_addicks Posts: 15,442
    edited January 2017
    Are we talking about real life percentages, or just the Boy/Girl paradox question?

    If so, it's a 1/3.
  • Leuth
    Leuth Posts: 23,312
    This isn't the Monty Hall problem as far as I can tell
  • Chizz
    Chizz Posts: 28,329
    Leuth said:

    If they had two boys they'd have said 'two boys' not two children. 100% a girl

    I like that answer. Of all the wrong ones so far, it's the most interesting.
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  • smudge7946
    smudge7946 Posts: 4,131
    33%
  • LoOkOuT
    LoOkOuT Posts: 10,853
    Chizz said:

    Leuth said:

    If they had two boys they'd have said 'two boys' not two children. 100% a girl

    I like that answer. Of all the wrong ones so far, it's the most interesting.
    Depends on how you know that the eldest is a boy. If they told you, then Leuth is likely right. But if you found out another way, then that's not an indicator and has no bearing on the likelihood either way.
  • bobmunro
    bobmunro Posts: 20,840
    edited January 2017
    Leuth said:

    This isn't the Monty Hall problem as far as I can tell

    No it isn't the Monty Hall problem - similar logic but different probability theory - Monty Hall is based on a second event having no bearing on the first event's probability.
  • 75%
  • As the previous fertilisation has no relationship to the principal of probability, the chances of the second and subsequent children being male are still 1:1 or 50:50.
  • Chizz
    Chizz Posts: 28,329

    75%

    Can you explain how you reached that answer?
  • bobmunro
    bobmunro Posts: 20,840
    Chizz said:

    75%

    Can you explain how you reached that answer?
    I think it was probably something like adding up scrabble scores for the letters in his forum name and taking away the number he first thought of!

    The answer is 1/3 or 33.333% change of being a boy - that's the only correct answer (although I like the thinking of some posters!)
  • Meiosis in males produces an equal ratio of gametes containing the x or Y chromosome. The female gamete has always got the X chromosome. On ejaculation therefore an equal proportion of male x and Y chromosomes are released. Therefore the chances of a male being conceived is always 1:1.
  • If he's in the dog house, then 0% on either sex.

    Other than that 50%
  • stackitsteve
    stackitsteve Posts: 12,102
    Leuth said:

    If they had two boys they'd have said 'two boys' not two children. 100% a girl

    Exactly what I was going to say