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9 August, 11:46

4. The density and strength of concrete are determined by the ratio of cement and aggregate. Suppose that a contractor has 480 cubic feet of a dry concrete mixture that is 70% sand by volume. How much pure sand must be added to form a new mixture that is 75% sand by volume?

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  1. 9 August, 13:08
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    The answer is 96ft^3

    Explanation:

    T=initial concrete mixture

    S1 = initial amount of sand

    S2=final amount of sand

    T2=final amount concrete mixture

    C=amount of cement

    dа ta:

    T=480Ft^3

    the quantities of the initial mixture are

    S=0.7*480=336Ft^3

    C=0.3*480=144 Ft^3

    we pose the following equations

    144+S2=T2

    T2*0.75=S2

    if we solve

    S2=144 / (1/0.75-1) = 432ft^3

    to know how much we should add we subtract it from the initial amount of sand

    Answer=432ft^3-336ft^3=96ft^3
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