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Math Help - Quartiles of a grouped frequency

  1. #1
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    Quartiles of a grouped frequency

    For the set of data given below find or estimate, as appropriate, the quartiles.

    Class| 1-9 | 10-19 | 20-29 | 30-39 | 40-49 | 50-59 | 60-69
    Frequency| 3 | 6 | 12 | 18 | 10 | 4 | 2



    Here is my work

    Cumulative frequency|
    3 | 9 | 21 | 39 | 49 | 53 | 55

    Since n=55
    So: Q₁ = b + {(¼ n – f)/fc} * c
    = 19.5 + {(1/4 (55) – 9)/12} * 9 = 23.06

    And Q₃ = 39.5 +{( ¾(55) – 39)/10} * 9 = 41.53

    So my answers are Q₁ = 23.06 & Q₃ = 41.53

    For this question, is it necessary to work for Q2? So far I know Q2 is median.
    There is another problem; my answers are not accurate as per my book’s answer. It says 23.46 & 41.75. So where is the problem? Please help me.
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  2. #2
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    Oppsssssssssss...........

    I'm stupid. Class width, c, will be 10.
    Last edited by geton; October 1st 2008 at 05:20 PM.
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