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Math Help - simultaneus equations help

  1. #1
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    simultaneus equations help

    http://www.emaths.co.uk/sats/2009/2009_68_Paper1.pdf go to link and to question 17 help me solve it.
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  2. #2
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  3. #3
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    3x+6y=30
    x+6y=20

    See how there are 2 6y's? You can subtract the two equations from each other to get rid of the 6ys/

    2x=10

    x=5 Now you have x=5 just substitute it back into any equation to find y.

    What I did was 3x-x = 2x and 30-20=10 The 6y cancelled each other.
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  4. #4
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    jharkhand
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    3x + 6y = 30... (1)
    x + 6y = 20.....(2)

    Multiply (2) by - on both sides
    => -(x+6y)=-20
    => -x - 6y = -20....(2)

    Then, on solving (1) & (2)-
    3x+6y = 30
    -x - 6y = -20

    +6y and -6y gets cancelled...
    so.. we get 3x= 30..(1)
    -x= -20..(2)
    (1) + (2)
    3x-x = 30-20
    => 2x=10
    => x=5

    Subsituting x in any of the two equations.-
    3x+6y = 30
    => 3 x 5 + 6y = 30
    => 15+6y = 30
    => 6y= 30-15
    => y= 15/6
    => y = 2.5
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