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What does x =? Helpp!

This topic has 1 expert reply and 4 member replies
gmatpup Senior | Next Rank: 100 Posts Default Avatar
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What does x =? Helpp!

Post Mon Nov 21, 2011 4:46 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    If x(2x+1)=0 and (x + 1/2)(2x - 3)=0, then x =?

    A. -3
    B. -1/2
    C. 0
    D. 1/2
    E. 3/2

    Answer is B

    Please explain how to do this type of question. Thank you Smile!

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    Post Mon Nov 21, 2011 4:53 am
    gmatpup wrote:
    If x(2x+1)=0 and (x + 1/2)(2x - 3)=0, then x = ?

    A. -3
    B. -1/2
    C. 0
    D. 1/2
    E. 3/2

    Answer is B

    Please explain how to do this type of question. Thank you Smile!
    You can substitute all answer choices to get the correct answer. Only B satisfies both the given equations.

    (-1/2)[2(-1/2) + 1] = 0 and (-1/2 + 1/2)[2(-1/2) - 3] = 0 holds true.

    The correct answer is B.

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    gmatpup Senior | Next Rank: 100 Posts Default Avatar
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    Post Mon Nov 21, 2011 1:03 pm
    I don't see how it holds true Sad When I do the calculation they do not equal 0.

    Please help!

    neelgandham Community Manager
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    Post Mon Nov 21, 2011 4:28 pm
    gmatpup wrote:
    If x(2x+1)=0 and (x + 1/2)(2x - 3)=0, then x =?

    A. -3
    B. -1/2
    C. 0
    D. 1/2
    E. 3/2

    Answer is B
    Please explain how to do this type of question. Thank you Smile!
    gmatpup,

    Let us solve for x here
    x(2x+1)=0 => x = 0 or 2x+1 = 0 => x = 0 or x = -1/2
    (x + 1/2)(2x - 3)=0 => x + 1/2 = 0 or 2x - 3 = 0 => x =-1/2 or x =3/2

    x=-1/2 satisfies both the equations Option
    Quote:
    B

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    rooster Senior | Next Rank: 100 Posts Default Avatar
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    Post Mon Nov 21, 2011 11:07 pm
    Two ways other than plugging in.

    1. Solve for zero:

    x(2x+1)=0 and (x + 1/2)(2x - 3)=0, then x =?

    In the first equation, you know x= 0 or 2x+1=0, x=-1/2

    In the second, in order for it to be zero, x needs to be -1/2 or 3/2.

    In order for a term to satisfy both equations, x=-1/2.


    OR

    Since you know the two are the both equal to zero, you can set them to each other

    x(2x+1)=0 and (x + 1/2)(2x - 3)=0, then x =?

    x(2x+1)=(x + 1/2)(2x - 3)

    2x^2 + x = 2x^2 -3x + x - 3/2

    x = -3x + x - 3/2

    3x = -3/2

    x= -1/2

    bookjive Newbie | Next Rank: 10 Posts Default Avatar
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    Posted:
    3 messages
    Post Thu Jan 05, 2012 8:40 pm
    How come you don't use the quadratic equation idea on this problem and FOIL? Is it just too slow?

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