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    drdee's Avatar
    drdee Posts: 1, Reputation: 1
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    #1

    Feb 16, 2011, 06:17 PM
    Can anyone help a 9th grader with algebra?
    How do you set up this story problem? Elijah sold 25 cds and dvds. He made 4 dollars off every cd and lost 1 dollar off every dvd. He made 25 dollars total. How many of each did he sell?
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Feb 17, 2011, 07:34 AM

    Set up 2 equations in 2 unkowns. Let C = number of CDs and let D = number of DVDs. He sold 25 total discs, so:

    C+D = 25

    And he made $25 profit:
    4C +(-1)D = 25

    Rearrange that second equation:

    4C -D = 25.

    To solve, note that if you add the first equation to the second the D's cancel out, so you can find a value for C. Then plug that value for C back into either of the two equations to find D. Can you take it from here?

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