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26 April, 11:43

David bought 3 dvds and 4 books for $40 at a yard sale. Anna bought 1 dvd and 6 books for $18. How much did each dvd and book cost?

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  1. 26 April, 12:12
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    A book is worth $1 and a DVD is worth $12.

    Step-by-step explanation:

    The equations (2 unknowns and two equations, d is for a DVD and b is for a book):

    For David: 3d+4b=40

    For Anna: d+6b=18

    Now multiply the second equation with - 3 and add to the first equation:

    3d+4b=40

    -3d-18b=-54

    Combined equation: - 14b=-14 and b=1 (means that each book is worth $1).

    Now for DVD price, use the second equation:

    d=18-6 or d=12 (means that each DVD is worth $12).

    A book is worth $1 and a DVD is worth $12.
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