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Math Help - Lisa is older than...

  1. #1
    Senior Member Paze's Avatar
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    Lisa is older than...

    Lisa is four times older than Anne.

    In 5 years, Lisa will be 3 times older than Anne.

    How old are Lisa and Anne?

    I've tried setting it up two ways: y=4x\\y+5=3x and then solving for x which grants me x=-5.

    I've also tried 4x+5=3x which also delivers the answer x=-5. Obviously Anne is not -5 years old.

    Thank you
    Last edited by Paze; February 22nd 2013 at 08:04 AM.
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  2. #2
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    Re: Lisa is older than...

    The first equation is correct. I think you want  y+5 = 3(x+5) for the second equation.
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  3. #3
    Senior Member Paze's Avatar
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    Re: Lisa is older than...

    I get the answer -5. How is that correct?

    Thank you.
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    Re: Lisa is older than...

    The first equation I am referring to is y=4x. To summarize, the equations are y=4x and y+5=3(x+5). So x=10.
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  5. #5
    Senior Member Paze's Avatar
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    Re: Lisa is older than...

    Quote Originally Posted by heaviside View Post
    The first equation I am referring to is y=4x. To summarize, the equations are y=4x and y+5=3(x+5). So x=10.
    Ah, I see. Thank you!
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    Re: Lisa is older than...

    Notice that the question asked "How old are Lisa and Anne". Just answering "x= 10" would NOT be acceptable. You started by saying that "Lisa is four times older than Anne" turned into y= 4x so apparently you are saying that Annes current age is 10 and Lisa's current age is 4(10)= 40.

    By the way, I would argue that y= 4x would be "Lisa is four times as old as Anne". I would interpret "Lisa is four times older than Anne" as meaning that the difference between Anne and Lisa's age is four times Anne's age. That would translate to y- x= 4x or y= 5x.
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  7. #7
    Senior Member Paze's Avatar
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    Re: Lisa is older than...

    Quote Originally Posted by HallsofIvy View Post
    Notice that the question asked "How old are Lisa and Anne". Just answering "x= 10" would NOT be acceptable. You started by saying that "Lisa is four times older than Anne" turned into y= 4x so apparently you are saying that Annes current age is 10 and Lisa's current age is 4(10)= 40.

    By the way, I would argue that y= 4x would be "Lisa is four times as old as Anne". I would interpret "Lisa is four times older than Anne" as meaning that the difference between Anne and Lisa's age is four times Anne's age. That would translate to y- x= 4x or y= 5x.
    Yea, sorry about the grammatical errors. I am translating the question from my own language Thank you.
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