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Math Help - Confused

  1. #1
    Newbie
    Joined
    Oct 2005
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    8

    Confused

    I need help with a problem.

    I worked it out but I think I'm wrong. Can some one please help solve this correctly?

    Use substitution to solve: 2x + y = 7
    5x - 2y = 4


    My answer:

    y = 7 - 2x
    7x - (7-2x) = 11
    7x - 7 + 2x = 11
    2 7
    9x 18
    9x/9 = 18/9
    y=2

    5x - 2y = 4
    5x-2(2)=4
    this is where I'm lost.

    Can someone help me.
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  2. #2
    MHF Contributor
    Joined
    Apr 2005
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    you were doing fine until
    "...9x/9 = 18/9
    y=2"

    You were solving for x and then you said y = 2?
    Should it not be x = 2?
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  3. #3
    Newbie
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    Oct 2005
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    Ok thank you.

    so that is x = 2

    then:

    5x - 2y = 4
    5(2) - 2y = 4
    10 - 2y = 4
    2y = 14

    y = 7
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  4. #4
    MHF Contributor
    Joined
    Apr 2005
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    No.
    y = 3.

    Why is
    2y = 14 ?

    5x - 2y = 4
    5(2) - 2y = 4
    10 - 2y = 4
    -2y = 4 -10
    -2y = -6
    y = -6 / -2
    y = 3
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  5. #5
    Newbie
    Joined
    Oct 2005
    Posts
    8

    Talking

    O.i.c where I made my mistake. THank you for the help.
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