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A question regarding "Who is born earlier in time"

  1. Jan 24, 2016 #1
    http://math.stackexchange.com/questions/1625487/who-is-born-earlier-in-time-the-great-grandson-of-the-grandson-or-the-grandson [Broken]
     
    Last edited by a moderator: May 7, 2017
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  3. Jan 24, 2016 #2

    phinds

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    How would you go about figuring this out (hint: it's trivial)
     
  4. Jan 24, 2016 #3

    DaveC426913

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    Actually, there is insufficient information. There's no way to tell which one was born earlier.

    I sure hope this isn't a homework question...
     
  5. Jan 24, 2016 #4
    I have found the question here: http://math.stackexchange.com/questions/1625487/who-is-born-earlier-in-time-the-great-grandson-of-the-grandson-or-the-grandson [Broken] a place where the moderators considered it ill-defined, quote: "You need to study the theory of definite descriptions to help you avoid posing ill-defined questions."

    In my opinion the problem has at least a nice solution.
     
    Last edited by a moderator: May 7, 2017
  6. Jan 24, 2016 #5

    DaveC426913

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    Yup. It is insufficiently defined to provide an answer.

    phinds has egg on his face. He thought the answer was trivial. but right about now, he's realizing he went off half-cocked. :smile:
     
  7. Jan 24, 2016 #6
    Just propose an answer, a solution, for a particular case of your choice.
     
  8. Jan 24, 2016 #7

    DaveC426913

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    Since the question cannot be answered as it stands, how is one supposed to answer it?

    The only correct answer is: I don't know, and neither do you.
     
  9. Jan 24, 2016 #8
    Take the case "one child policy".
     
  10. Jan 24, 2016 #9

    DaveC426913

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    There you go! That must be specified in the question.

    And now the question is trivial.
     
  11. Jan 24, 2016 #10

    phinds

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    No, I made a simplifying assumption that the ages at which everyone had their so was the same. That makes it trivial. The point is to simply count generations. A better-formed question would be "how many generations is that" and that is trivial.
     
  12. Jan 24, 2016 #11

    phinds

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    No, not YOU have egg on your face, at least to the same extent that I did. You have made the same simplifying assumption I did.
     
  13. Jan 24, 2016 #12

    DaveC426913

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    Why have you
    a] made an unfounded assumption, and
    b] completely reformulated the question,
    c] without stating your case-reducing assumption in the answer (necessary to make it correct)?
     
    Last edited: Jan 24, 2016
  14. Jan 24, 2016 #13

    DaveC426913

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    No I didn't.

    The OP provided the missing criterion in post 8. 'One child policy' means that the answer is so trivial it is degenerate (Which is younger: Person A or the same person?) I'm not sure why you think I made any simplifying assumptions.
     
  15. Jan 24, 2016 #14

    phinds

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    But the one child criterion does not make for a unique answer. You have to make the simplifying assumption of same age births. Think it through, you'll get it. Assume all births are after a different number of years. Clearly you don't end up w/ the same answer (necessarily).
     
  16. Jan 24, 2016 #15

    DaveC426913

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    Yes it does.

    You are comparing the age of a person to themselves. They are the same person.

    I think you might have overlooked the last criterion in the OP: the ancestor is the same person in both scenarios.
     
  17. Jan 24, 2016 #16

    phinds

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    You're missing the point. Write it out, using different ages for each person when their son is born. You get different answers and which path leads to a younger person will vary depending on those ages.
     
  18. Jan 24, 2016 #17

    DaveC426913

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    See post 15.
     
  19. Jan 24, 2016 #18

    phinds

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    Yeah, you're right. I goofed. Definitely egg on my face, not yours. Thanks. o:)
     
  20. Jan 24, 2016 #19

    DaveC426913

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    It's a really tricky one!
     
  21. Jan 24, 2016 #20

    phinds

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    Doesn't seem all that tricky if you think it through properly, which I did not at first.
     
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