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Math Help - Common ratio problems

  1. #1
    Junior Member
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    Exclamation Common ratio problems

    been stuck on thesse for a while now.
    Solve for the missing variable and find the common ratio. ( these are two diffrent problems)
    1.)  I run into trouble just afte I cross multiply<br />
X-3, X+1 ,4X-2<br />
    answer r=3 & R=-1/2

    2.) <br />
X, 10, 25X<br />
    answer r=5 r=-5
    Last edited by nightrider456; March 3rd 2010 at 08:26 PM.
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  2. #2
    MHF Contributor
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    If we KNOW there is a geometric sequence, division with any two consecutive values should produce the same result.

    Let's try this one: 1, 2, 4, 6, 16

    Notice: 2/1 = 2 and 4/2 = 2 and 8/4 = 2 and etc.

    With your problem #1, we have:



    So, \frac{X+1}{X-3}\;=\;RATIO

    and \frac{4X-2}{X+1}\;=\;RATIO

    Therefore: \frac{X+1}{X-3}\;=\;\frac{4X-2}{X+1}

    I think it's wonderful that we used the common ratio to help solve for the missing variable value, but we did NOT yet solve for the common ratio.
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