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Math Help - Interquartile range

  1. #1
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    Interquartile range

    Hi everyone

    Please take a look at this image

    http://www.ernestround.co.uk/cfd.png


    I would work the median out as the value at 1.8
    I would work out the LQ starting at 1.3
    I would work out the UQ ending at 2.3

    However, when I read the answer sheet it says that the IQR is 2.1 - 1.6

    I don't understand how this could be the case. Can anyone explain it to me please?


    Thanks

    Pete
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  2. #2
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    Quote Originally Posted by mrpmorris View Post
    Hi everyone

    Please take a look at this image

    http://www.ernestround.co.uk/cfd.png


    I would work the median out as the value at 1.8
    I would work out the LQ starting at 1.3
    I would work out the UQ ending at 2.3

    However, when I read the answer sheet it says that the IQR is 2.1 - 1.6

    I don't understand how this could be the case. Can anyone explain it to me please?


    Thanks

    Pete
    You do know that LQ is the 25th percentile, yes? So read across from cumulative frequency = 25 until you hit the curve. Then you go down. Down in fact to 1.6 .... It's quite plain to see .....

    Similarly, You do know that UQ is the 75th percentile, yes? So read across from cumulative frequency = 75 until you hit the curve. Then you go down. Down in fact to just a shade under 2.1 .... Again, it's quite plain to see .....

    I have no idea how you got your values - you're way off .....
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  3. #3
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    Doh!

    Of course! I was looking at 25% and 75% across the horizontal axis and not along the cumulative frequency!


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