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Math Help - Finding the number of red disks

  1. #1
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    Finding the number of red disks

    Mike has 72 solid-colored disks that are either red, blue, or green. Once lined up, he finds that there are 15 more red disks than green and 9 more green disks than blue. How many red disks does he have?

    I know the answer is 37 but I don't see how to set it up.
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  2. #2
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    Re: Finding the number of red disks

    Quote Originally Posted by dannyc View Post
    Mike has 72 solid-colored disks that are either red, blue, or green. Once lined up, he finds that there are 15 more red disks than green and 9 more green disks than blue. How many red disks does he have?

    I know the answer is 37 but I don't see how to set it up.
    number of red = x
    number of green = x-15
    number of blue = x-15-9 = x-24

    Then x+x+x-15-24 = 72
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  3. #3
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    Re: Finding the number of red disks

    Quote Originally Posted by dannyc View Post
    Mike has 72 solid-colored disks that are either red, blue, or green. Once lined up, he finds that there are 15 more red disks than green and 9 more green disks than blue. How many red disks does he have? I know the answer is 37 but I don't see how to set it up.
    \begin{align*}r &=g+15\\ g &= b+9\\ r+g+b &=72   \end{align*}
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