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Can someone help me solve the following problems using the substituion method? I need to find the ordered pairs and I do not get it.... Here they are

1)
6m+n=47
m-4n=12

2)
6x+4y=-10
-7x+y=57

3)
5x+7y=43
-4x+y=25

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Kristin

  1. I use substitution when I notice that in one of the equations one of the variables has a coefficient of 1
    Then solve for that single variable
    e.g. in #2
    -7x + y = 57 ,
    y = 7x + 57

    now sub that into the other equation
    6x + 4y = -10
    6x + 4(7x+57) = 10
    6x + 28x + 225 = 10
    34x = - 218
    x = -218/34 = - 109/17
    then y = 7(-109/17) + 57
    y = 206/17

    do the other two the same way

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    Reiny

  2. Okay but the homework is saying the answer is (-7,8) so how would they have gotten that from the equation you did above?

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    Kristin

  4. I made a transcript error.

    After 6x + 4(7x+57) = 10 it should have been
    6x + 28x + 228 = -10

    I had 2 errors in copying that line, sorry about that
    Now i works out

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    Reiny

  5. Okay so what about number one it is a + and the a - for the second problem how do you figure a subtitution problem like that? do the signs make a difference?

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    Kristin

  6. For number 3 I got (6.7,51.8) is this correct?

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    Kristin

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