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Math Help - Find Expression for Cost y

  1. #1
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    Find Expression for Cost y

    A 50 cm length of ribbon costs x dollars. Find an expression for the cost of y meters of ribbon. Give your answer to its simplest form.

    My solution:

    Let y = the total cost for a certain amount of x ribbons

    Let x = the cost per ribbon

    I write a linear equation to express a relation between x, y and 50.

    I say the equation is y = 50x.

    Is this correct? If not, why not?
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  2. #2
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    Re: Find Expression for Cost y

    Quote Originally Posted by nycmath View Post
    A 50 cm length of ribbon costs x dollars. Find an expression for the cost of y meters of ribbon. Give your answer to its simplest form.

    My solution:

    Let y = the total cost for a certain amount of x ribbons

    Let x = the cost per ribbon

    I write a linear equation to express a relation between x, y and 50.

    I say the equation is y = 50x.

    Is this correct? If not, why not?
    It looks good to me. However the 50 is in cm, while y is to be measured in m.

    -Dan
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  3. #3
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    Re: Find Expression for Cost y

    Quote Originally Posted by nycmath View Post
    A 50 cm length of ribbon costs x dollars. Find an expression for the cost of y meters of ribbon. Give your answer to its simplest form.

    My solution:

    Let y = the total cost for a certain amount of x ribbons

    Let x = the cost per ribbon

    I write a linear equation to express a relation between x, y and 50.

    I say the equation is y = 50x.

    Is this correct? If not, why not?
    The cost x dollars is for 50 cm. You need first to convert those to m. Yhen use that number to calculate the cost of y meters.
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  4. #4
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    Re: Find Expression for Cost y

    You say "y = the total cost for a certain amount of x ribbons" and "Let x = the cost per ribbon"

    So is "x" a number of ribbons or the cost per ribbon?

    In your "y= 50x" what does "x" represent?
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    Re: Find Expression for Cost y

    Quote Originally Posted by HallsofIvy View Post
    You say "y = the total cost for a certain amount of x ribbons" and "Let x = the cost per ribbon"

    So is "x" a number of ribbons or the cost per ribbon?

    In your "y= 50x" what does "x" represent?
    OP question is x is the cost of 50 cm, or 0.5 m. from which you get the cost of one meter is x/0.5 = 2x. The cost of y meters would be..

    y is the cost of a number of meters of ribbon, not the number of ribbons
    Last edited by votan; September 28th 2013 at 02:36 PM.
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  6. #6
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    Re: Find Expression for Cost y

    Quote Originally Posted by votan View Post
    OP question is x is the cost of 50 cm, or 0.5 m. from which you get the cost of one meter is x/0.5 = 2x. The cost of y meters would be..

    y is the cost of a number of meters of ribbon, not the number of ribbons
    You got that from
    "Let y = the total cost for a certain amount of x ribbons

    Let x = the cost per ribbon"

    I'm impressed!
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  7. #7
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    Re: Find Expression for Cost y

    Quote Originally Posted by HallsofIvy View Post
    You got that from
    "Let y = the total cost for a certain amount of x ribbons

    Let x = the cost per ribbon"

    I'm impressed!
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  8. #8
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    Re: Find Expression for Cost y

    Isn't everyone? My point was that your initial statement of the problem was very confused, using "x" for two different things. But Votan was able to make sense of it!
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