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A logical question

  1. Sep 13, 2008 #1
    alton,yiber,mobi,sera are sitting on a bench
    three out of four of these arguments are needed in order to deside
    the location of eah person.

    wich one of these arguments does not needed?

    A.mobi sits between sera and alton.
    B.yiber sits on the right from alton and sera
    C.mobi sits close to alton
    D.sera sits on the right from alton

    in a previos femiliar question that i asked here
    we found that one argument can be found from another argument

    S M A
    A M S




    argument 4 can be found from argument 1
    which means that 4 is not needed

    this is the only pair of arguments which have similarities

    the answer is argument 3
    where is my mistake?
  2. jcsd
  3. Sep 14, 2008 #2


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    You have correctly provided two hypotheses for argument 1. Argument 4 discards the first hypothesis, so it is needed.
    Argument 2 says that Y is not between A and S, so the order must be AMSY. Argument 3 is not needed.
  4. Sep 15, 2008 #3
    you sayd
    "Argument 4 discards the first hypothesis"
    whats the first hypothesis?
    did you meen the first argument?

    my point is if we can find the data of argument 4 in argument 1

    then argument 1 is not needed

    is that correct?
  5. Sep 15, 2008 #4


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    No, you proposed 2 hypotheses for argument 1: SMA and AMS. Argument 4 discards SMA. It remains only AMS. If you did not have argument 4, you could not eliminate any of them.
  6. Sep 15, 2008 #5
    Yes. If you can find the exact data from (D) within (A), then (D) is not needed. But! You can't find (D) within (A), so (D) is needed.

    However, look at (A) and (C). (A) says that Mobi is between Sera and Alton. Therefore, ONLY looking at (A), we know that the situation is one of:


    We don't know which one is true yet (because we've only looked at (A)), but we know it's one of those 4 possibilities.

    Now look at (C). It says that Mobi sits next to Alton. But we already knew that with (A)! If you look at all the examples in (A) that are possible, EVERY SINGLE ONE has Mobi and Alton sitting next to each other. Therefore, since (C) told us nothing new, and told us LESS than (A), we know that (C) is unnecessary.

  7. Sep 15, 2008 #6


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    Not really. Without statement B, you could also have:
    In two of those you have A and M close to each other.
  8. Sep 15, 2008 #7
    This gets into the tricky parts of language. I suspect that transgalactic's native language is not English, and that s/he's transcribing these problems from one language to ours. If not, these problems are very unclear in their writing. For instance, "mobi sits close to alton" is ambiguous. "Close" is a relative term. Hence, if there is one person between Mobi and Alton, that's still arguably "close", even though I assume that by "close" they mean "next to".

    Anyway, suffice to say that I assumed that (A) meant "Mobi sits directly between Sera and Alton". If you don't assume that, the problem is slightly more difficult to prove, but still possible.

    Regardless of which interpretation of (A) you choose:

    Ignoring none of them gives you ONLY: AMSY
    Ignoring (A) gives you possibilities: AMSY or MASY
    Ignoring (B) gives you possibilities: AMSY or YAMS
    Ignoring (C) gives you ONLY: AMSY
    Ignoring (D) gives you possibilities: AMSY or SMAY

  9. Sep 15, 2008 #8


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    My native language is not English either. I was born and live in Brazil, so may be I misinterpreted the question. Anyway, my conclusion is the same you got: (C) is superfluous.
  10. Sep 21, 2008 #9
    c is not needed
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