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Logical question

  1. Aug 11, 2008 #1
    data:
    the snake of goerge is the longest water snake in the world.
    the snake of shon in the longest black snake in the world.

    which one of the answers can be concluded from the data?

    1.the snake of goerge is not black,and the snake of shon is not a water snake
    2.if the snake of george is not black then the snake of shon is a water snake
    3.if the snake of shon is a water snake then the snake of george is not black
    4.if the snake of shon is a water snake then the snake of george is black
     
  2. jcsd
  3. Aug 11, 2008 #2

    arildno

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    To the others in Brain teasers forum:
    I suggested to some one that he might get help from you guys here, so treat this less as a challenge to be answered forthwith than a homework problem OP can work through.

    Take a crack at 1, some one:

    This says that TWO distinct property holds.
    Which two are those?
    And, BOTH of those must be true if you were to be able to conclude it from the data. MUST both true, or must only one be true, or neither of the statements must be true?
     
  4. Aug 11, 2008 #3
    i canceled the first and the second statement
    because they could have also the other property
    although not being the longest snake for tis property

    but regarding the third and the 4th answers
    i cant understand how can they link that if one snake has some property
    then it affects the properties of the other???
     
  5. Aug 11, 2008 #4

    arildno

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    Well, take 3 (and 4).
    If shon's snake is a water snake, then that means shon's black water snake is the longest black water snake in the world.
    (after all, it is the longest of all black snakes, hence longer than any other black water snakes..)
    Can therefore george's water snake be black and still remain the longest water snake?
    3 says no to that, 4 says yes.
    Which is the correct answer?
     
  6. Aug 11, 2008 #5
    the answer is 3
    i cant understand why its 3

    if shons snake is also a water snake
    so he is the longest black snake but
    not the longest water snake

    so goerges snake can be the longest water snake but not the longest black snake

    those two options do not collide with one another

    why geoges snake cannot be black??
     
  7. Aug 11, 2008 #6

    arildno

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    Sure it does!

    Remember that george has the longest water snake.

    If shon's snake is a water snake, it has to be shorter than george's snake (agreed?) (*)

    But, we know that shon's snake is the longest of black snakes.
    Therefore, IF george's snake is black, then it must be shorter than shon's (**)

    (*) and (**) contradict each other.

    Therefore, (**) cannot be true, since (*) is true by assumption.

    Therefore, george's snake cannot be black if shon's snake is a water snake.
     
  8. Aug 11, 2008 #7
    the answer is 3

    if shon's snake is a water snake then it is the longest black snake but must be SHORTER than george's snake,now, if george's snake is a black snake than it's the longest water snake but it must be SHORTER than shon's snake, but it can't be because shon's snake is already shorter than george's snake -> hence george snake ain't black
     
    Last edited: Aug 11, 2008
  9. Aug 12, 2008 #8
    i got it
    thanks
     
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