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June 22nd 2005 - The Official S2 Discussion Thread! watch

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    Oh well, 9 or 10... got kinda confuzzled doing everything backwards. Method marks all round!
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    why was it not 10??? loadsa ppl got 9 or 10, and a few ppl even got 11? wot was the working for that question???
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    im sure it was postive skew as the median was greater then the mode and also the mean.
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    when n=20 and P=0.25
    P(X<<10)=0.9961>0.99

    therefore n=20-10=10...?
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    (Original post by riks2004)
    im sure it was postive skew as the median was greater then the mode and also the mean.

    na..........

    Mode> median>mean

    therefore negative skew
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    i got root 2 for median i factorised it so (m^2 - 2 )(m^2 - 2) = 0
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    why not 11 - no way it can be 10 i think, because you have to do the c-1 thing dont you? i.e. 9 if you didn't flip, and 11 if you did, i got something like y>=8 or something and then got 9 from that donig c-1=8, then i thought we had to flip again because you are interseted in the number of successes and not the number of untreated cases - well i did something like that...hopefully will get some marks - i need a high A in this mod cos i messed up my P5 on monday:eek:

    got to revise for P4, P6, M4 next week:eek:(

    phil
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    guys u need to specify if its x<9 or less or equal too.

    as x<10 is the same as x is less or equal to 9.

    i got x<9 or x is less or equal to 8.
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    (Original post by riks2004)
    i got root 2 for median
    no way that can be right - its def 1.08, cos you get 0.5 when you sub this into the cdf - i checked it
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    (Original post by tiantang)
    guys u need to specify if its x<9 or less or equal too.

    as x<10 is the same as x is less or equal to 9.

    i got x<9 or x is less or equal to 8.

    the question asked for the maximum value!
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    (Original post by tiantang)
    guys u need to specify if its x<9 or less or equal too.

    as x<10 is the same as x is less or equal to 9.

    i got x<9 or x is less or equal to 8.
    was a very cnofusign two questions huh? i did the rest of the paper in 0.5 hours, and spent an hour thinking about that one:eek: - and still think i got it wrong
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    (Original post by Phil23)
    no way that can be right - its def 1.08, cos you get 0.5 when you sub this into the cdf - i checked it

    i disagree im sure it was root 2, any1 got the paper so we can check
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    (Original post by Savioahang)
    the question asked for the maximum value!
    right hope i dont marks knocked off - i only gave critical region - hope markers are not stingy about minor details
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    Last question:

    For successful recovery less than 75% , not recovered has to be greater than 25%.

    x-Bi(20, 0.25)

    Therefore (x 'greater or equal to' c) is < 1%
    (x 'smaller or equal to c-1')>99%

    from tables c-1=10, c=11

    therefore x 'greater or equal to' 11 or more people who DO NOT recover!

    therefore for people who DO recover.

    x 'smaller or equal to 9.

    For the cdf question:

    mean was 1/1/15
    mode was root (4/3)- you had let 'x^2' equal 'y' to get a normal quadratic equation.

    and the pdf was defiantely negatively skewed as mean<median<mode
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    (Original post by Phil23)
    no way that can be right - its def 1.08, cos you get 0.5 when you sub this into the cdf - i checked it
    i got √3 for one of them think it was the mode :confused:
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    (Original post by marisad_uk)
    i got √3 for one of them think it was the mode :confused:
    i got rt (4/3) for that:eek:
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    (Original post by tiantang)
    For successful recovery less than 75% , not recovered has to be greater than 25%.

    x-Bi(20, 0.25)

    Therefore (x 'greater or equal to' c) is < 1%
    (x 'smaller or equal to c-1')>99%

    from tables c-1=10, c=11

    therefore x 'greater or equal to' 11 or more people who DO NOT recover!

    therefore for people who DO recover.

    x 'smaller or equal to 9.
    from tables i got c-1=9 therefore c=10 and i just left it at x=10 for answer
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    (Original post by Phil23)
    i got rt (4/3) for that:eek:

    same
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    (Original post by marisad_uk)
    from tables i got c-1=9 therefore c=10 and i just left it at x=10 for answer
    if you did greater than 99% (which i believe is correct than it is c-1=10. I have just checked the tables at home.
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    YESSS! I got 9 for the last answer as well. And negative skew. Woooo! Oh and route 4/3.

    Best exam I've done so far hopefully it will make up for the disaster that was P3.
 
 
 
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