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{statics} Kvartil (quartiles) why I didnt get right solution ?

  1. Dec 8, 2014 #1
    1. The problem statement, all variables and given/known data

    On this vector I didnt get the right answer:

    x = [ 5 8 10 11 137 ]

    q3: i = (p/100)*n = (75/100)*5 = 3.75 >> 4th in vector is 11
    q1: i = (25/100)*5 = 1.25 >> 2nd is 8

    in MATLAB is solution
    Capture.PNG



    2. Relevant equations


    3. The attempt at a solution
     
  2. jcsd
  3. Dec 8, 2014 #2

    haruspex

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    Never seen this concept before, but from a little reading at http://au.mathworks.com/help/stats/quantiles-and-percentiles.html it seems that the vector is interpreted as:
    1/10 are <= 5
    3/10 are <= 8,
    5/10 are <= 10
    etc.
    For the first quartile, we want find how many are <= 0.25. This is done by interpolation between1/10 and 3/10. 0.25 is positioned (0.25-0.1)/(0.3-0.1) along that interval, so gets that share of (8-5):
    5 + (8-5)*(0.25-0.1)/(0.3-0.1) = 7.25.
     
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