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Math Help - Help

  1. #1
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    Help

    The base material for a certain roadbed is 80% crushed rock when measured by weight. How many tons of this material must be mixed with another material containing 30% rock to make 150 tons of material that is 40% crushed rock?
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  2. #2
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    Re: Help

    Hello, mbruiz1!

    The base material for a certain roadbed is 80% crushed rock when measured by weight.
    How many tons of this material must be mixed with another material containing 30% crushed rock
    to make 150 tons of material that is 40% crushed rock?

    Let x = tons of 80% material.
    This contains 0.8x tons of crushed rock.

    Let 150-x = tons of 30% material.
    This contains: 0.3(150-x) tons of crushed rock.

    The mixture will contain: 0.8x + 0.3(150-x) tons of crushed rock.


    But we know that the mixture will be 150 tons which is 40% crushed rock.
    . . It will contain: 0.4(150) \,=\,60 tons of crushed rock.


    We just described the final amount of crushed rock in two ways.

    There is our equaton! . . . 0.8x + 0.3(150-x) \;=\;60


    Got it?
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