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Math Help - Writing an algebraic equation

  1. #1
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    Writing an algebraic equation

    Subtract 5 from the sum of
    x and 7 times 3 and the result is 20.


    My answer is

    x-5 + 7 x 3 = 20

    x = 4 is that right?
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Patience View Post
    Subtract 5 from the sum of
    x and 7 times 3 and the result is 20.


    My answer is

    x-5 + 7 x 3 = 20

    x = 4 is that right?
    Is that exactly how the question was phrased? if so, i'd interpret it like this:

    3(x + 7) - 5 = 20
    => 3x + 21 -5 = 20
    => 3x + 16 = 20
    => 3x = 4
    => x = 4/3

    I dont think the "times 3" refers to only the 7 being multiplied by 3, I'm pretty sure they'd just say 21.
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  3. #3
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    Quote Originally Posted by Patience View Post
    Subtract 5 from the sum of
    x and 7 times 3 and the result is 20.


    My answer is
    x-5 + 7 x 3 = 20
    x = 4 is that right?
    Hi,

    your calculations are OK, but for me the following way is possible too:

    First calculate the sum: (x+7)
    The sum should be multiplicated by 3: (x+7)*3
    Subtract 5 from this product: (x+7)*3 - 5
    The result is 20:

    3*(x+7) - 5 = 20 Expand the bracket:
    3x + 21 - 5 = 20 Collect all constants at the RHS of the equation:

    3x = 20 - 21 + 5 = 4 Divide both sides by 3:

    x = 4/3

    EB
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    Yes that is the exact question.

    After looking at your calculation I am kinda lost.

    You say that x = 4/3

    How do you solve 4/3 to = 20?
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  5. #5
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Patience View Post
    Yes that is the exact question.

    After looking at your calculation I am kinda lost.

    You say that x = 4/3

    How do you solve 4/3 to = 20?
    By plugging it into the equation given:

    3(x + 7) - 5 = 3(4/3 + 7) - 5 = 4 + 21 - 5 = 25 - 5 = 20
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