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    • Thread Starter

    I've copied and pasted the question section below. Q6 part 6 in MEI exam S1 Jan 08. It asks to use the *** freq chart I have just made to work out the 90th percentile:

    "Use your graph to estimate the 90th percentile."

    But I have no idea how its getting 43.6 by using hours 166. I assume its working out the 90th hour and then using the diagram to estimate the *** freq... but I'm not sure. Please help

    The maximum temperatures x degrees Celsius recorded during each month of 2005 in Cambridge are
    given in the table below.
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    9.2 7.1 10.7 14.2 16.6 21.8 22.0 22.6 21.1 17.4 10.1 7.8
    These data are summarised by n = 12, Σ x = 180.6, Σ x2 = 3107.56.
    (i) Calculate the mean and standard deviation of the data. [3]
    (ii) Determine whether there are any outliers. [3]
    (iii) The formula y = 1.8x + 32 is used to convert degrees Celsius to degrees Fahrenheit. Find the
    mean and standard deviation of the 2005 maximum temperatures in degrees Fahrenheit. [3]
    (iv) In New York, the monthly maximum temperatures are recorded in degrees Fahrenheit. In 2005
    the mean was 63.7 and the standard deviation was 16.0. Briefly compare the maximum monthly
    temperatures in Cambridge and New York in 2005. [2]
    The total numbers of hours of sunshine recorded in Cambridge during the month of January for each
    of the last 48 years are summarised below.
    Hours h 70 ≤ h < 100 100 ≤ h < 110 110 ≤ h < 120 120 ≤ h < 150 150 ≤ h < 170 170 ≤ h < 190
    Number of years 6 8 10 11 10 3
    (v) Draw a cumulative frequency graph for these data. [5]
    (vi) Use your graph to estimate the 90th percentile.
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    Community Assistant
    (Original post by moak44)
    I assume its working out the 90th hour and then using the diagram to estimate the *** freq... but I'm not sure. Please help
    Do you know what percentile means?
    • Thread Starter

    I assumed percentile is essentially percentage. I wiki'd it, and it certainly comes across this way.

    There was a forumula n=p/100 * n + 0.5

    This doesn't help. There are 120 enteries (70 -> 190) which doesn't get me to any value the answer says:

    Line on graph at cf = 43.2(soi) or used
    90th percentile = 166

    Still not getting it :-/

    to find the upper quartile ( 75th percentile ) you go 75% up the cumulative frequency axis then draw a horizontal line to the curve, then go down to the x axis to read of the UQ...

    the 90th percentile is the same method but with 90% ( hence the mention of 43.2 in the answer scheme )
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Updated: December 31, 2012
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