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Is b < 0?

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james Just gettin' started! Default Avatar
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05 Oct 2014
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Is b < 0? Post Wed Oct 08, 2014 9:32 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    is b<0?

    (i) b is a multiple of 13
    (ii) b^3 < 13

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    Post Wed Oct 08, 2014 9:46 pm
    Hi james,

    This question is perfect for TESTing Values:

    We're asked if B < 0. This is a YES/NO question.

    Fact 1: B is a multiple of 13.

    By definition, a multiple can be positive, negative or 0.

    So B could be….
    13(1) = 13 Positive results gives us a NO answer
    13(2) = 26
    etc.

    13(0) = 0 "Null" result gives us a NO answer

    13(-1) = -13 Negative results give us a YES answer
    13(-2) = -26
    etc.
    Fact 1 is INSUFFICIENT.

    Fact 2: B^3 < 13

    Here we have no restrictions on "multiples", so any number that fits this restriction will do…

    If….
    B = 1, then the answer is NO
    B = -1, then the answer is YES
    Fact 2 is INSUFFICIENT

    Combined, we know…
    B is a multiple of 13
    B^3 < 13

    If B = 0, then the answer to the question is NO
    If B = -13, then the answer to the question is YES
    Combined, INSUFFICIENT

    Final Answer: E

    GMAT assassins aren't born, they're made,
    Rich

    _________________
    Contact Rich at Rich.C@empowergmat.com

    Post Fri Oct 10, 2014 5:04 am
    james wrote:
    Is b < 0?

    (i) b is a multiple of 13
    (ii) b³ < 13
    Target question: Is b negative?

    Statement 1: b is a multiple of 13
    Here are some multiples of 13: ....-39, -26, -13, 0, 13, 26, 39,...
    As you can seem there are several values of b that satisfy the given condition. Let's examine two of them that yield CONFLICTING answers to the target question:
    Case a: b = -13, in which case b IS negative
    Case b: b = 0, in which case b is NOT negative
    Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

    Statement 2: b³ < 13
    There are several values of b that satisfy this condition. Here are two:
    Case a: b = -1, in which case b IS negative
    Case b: b = 0, in which case b is NOT negative
    Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

    Statements 1 and 2 combined
    There are still several values of b that satisfy BOTH conditions. Here are two:
    Case a: b = -13, in which case b IS negative
    Case b: b = 0, in which case b is NOT negative
    KEY TAKEAWAY: 0 is a multiple of all integers
    Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

    Answer = E

    Cheers,
    Brent

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