math

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i need help with this problem x AND y ARE THE SAME IN BOTH PROBLEM????
7x+8y=25
9x+10Y=35

  • math -

    7x+8y=25 times 5 is 35 x + 40 y = 125
    9x+10y=35 times 4 is 36 x + 40 y = 140
    ++++++++++++++++++++++now subtract

    -1 x + 0 = -15
    so
    x = 15
    then
    7(15) + 8 y = 25
    105 + 8 y = 25
    8 y = -80
    y = -10

  • math -

    thanks but y\why did you multiply it by 4 and 5 at the begging

  • math -

    Because 40 is the least common multiple of 8 and 10
    I could have used the first times 9 and the second times 7 and eliminated x.

  • math -

    What method is this (like is it elimination,substiution)

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