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Math Help - Linear Equation In One Variable

  1. #1
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    Question Linear Equation In One Variable

    Can someone please help me with the following problem?

    5 years ago, mother was seven times as old as her son & 5 years hence, she will be three times as old as her son. Find their present ages.

    This is what I tried:

    Let present age of son be x.

    Five years ago:
    Son's age = x-5
    Mother's age = 7(x-5)

    Five years hence (means 5+5=10 years hence):
    Son's age = x-5+10 = x+5
    Mother's age = 7(x-5)+10 = 7x-35+10=7x-25

    Five years hence, mother will be three times as old as her son. So

    x+5 = 3(7x-25)
    x+5 = 21x-75
    20x = 80
    x = 4

    But the answer is wrong! What am I doing wrong?

    Thanks,

    Ron
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  2. #2
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    It should be 3(x+5) = 7x-25, not x+5 = 3(7x-25).
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  3. #3
    MHF Contributor
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    5 years ago, mother was seven times as old as her son
    m - 5 = 7(s - 5)

    5 years hence, she will be three times as old as her son
    m + 5 = 3(s + 5)
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