Hey there! Sign in to join this conversationNew here? Join for free

Edexcel S2 - 27th June 2016 AM Watch

  • View Poll Results: How did you find the Edexcel S2 exam?
    Very hard
    145
    14.71%
    Hard
    331
    33.57%
    Normal
    293
    29.72%
    Easy
    152
    15.42%
    Very easy
    65
    6.59%

    Offline

    1
    ReputationRep:
    Give me an easy and intuitive way to remember the skewness of a PDF please
    Offline

    2
    ReputationRep:
    (Original post by Lilly1234567890)
    if i have like three functions of CDF
    and i want to find the mean which function do i choose to equal to 0.5?
    I just use trial and error lol, if you've picked the wrong one then the x value you get won't make sense ☺️ I'd be interested to hear if anyone had a better system though!
    Offline

    2
    ReputationRep:
    (Original post by Patrick Gekko)
    I got the answer in the MS
    How?

    I have the same working out as the mark scheme but a different answer
    Offline

    2
    ReputationRep:
    Someone quickly help me pls....

    https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

    3a. Im getting x<<1 and x>>2
    • Very Important Poster
    • Thread Starter
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by Lilly1234567890)
    if i have like three functions of CDF
    and i want to find the mean which function do i choose to equal to 0.5?
    Are you asking about the median? You cannot find the mean in that way.
    Offline

    1
    ReputationRep:
    (Original post by khaleesi98)
    I just use trial and error lol, if you've picked the wrong one then the x value you get won't make sense ☺️ I'd be interested to hear if anyone had a better system though!
    I usually test the upper bound of the second function, since it probably wont be in the first function so testing that boundary tells whether its the second or the third.

    Such a small thing, but I think it saves a bit of time.
    Offline

    4
    ReputationRep:
    (Original post by RetroSpectro)
    How?

    I have the same working out as the mark scheme but a different answer
    Really? If you've got the same working as the MS then I'm not sure what has gone wrong.

    Obviously X is binomially distributed (120,0.008)
    You want the probability of there being at most 1 cracked egg, so this is P(x=0) + P(x=1)

    Then just use the formula in the formula book and you should get it..
    • Very Important Poster
    • Thread Starter
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by mangoli)
    Give me an easy and intuitive way to remember the skewness of a PDF please
    If you have the S1 textbook, there's like a page describing everthing.

    I just like to remember that mode < median < mean => positive skew, the opposite is negative.

    Mode, median, mean. Easy list to remember (in that order).
    Offline

    2
    ReputationRep:
    (Original post by RetroSpectro)
    How?

    I have the same working out as the mark scheme but a different answer
    Liink the MS pls
    Offline

    14
    ReputationRep:
    (Original post by SeanFM)
    Are you asking about the median? You cannot find the mean in that way.
    I thought if a CDF is symmertical then the median=mean?
    Offline

    1
    ReputationRep:
    (Original post by mangoli)
    Give me an easy and intuitive way to remember the skewness of a PDF please
    Way i remembered it in S1 is mean,median,mode: the mean wants to be as 'mean' as possible so when its bigger than the median and mode its positive (skew).

    It's an odd way to remember, but if it works, how odd really is it...
    Offline

    2
    ReputationRep:
    (Original post by Patrick Gekko)
    Really? If you've got the same working as the MS then I'm not sure what has gone wrong.

    Obviously X is binomially distributed (120,0.008)
    You want the probability of there being at most 1 cracked egg, so this is P(x=0) + P(x=1)

    Then just use the formula in the formula book and you should get it..
    Oh i think entering 120C0 in my calculator without brackets mixed up the order of the processes hence why i got a different answer.

    Thanks anyway
    Offline

    2
    ReputationRep:
    Hardest S2 papers please? X

    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

    Q4d and e?
    • Very Important Poster
    • Thread Starter
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by undercxver)
    I thought if a CDF is symmertical then the median=mean?

    Let's see with an example.

    If we had pdf = x for 0 <= x < 0.5 and 1-x for 0.5 <= x < 1 then the mode is 0.5.

    The CDF is x^2/2 for 0 <= x < 0.5 and x - (x^/2) + (1/8) for 0.5 =< x < 1 so the median is indeed the mode.

    The mean is integral of x between 1 and 0 which is 0.5.. so mode = median = mean. So we have shown that there is in fact no skew when all 3 of these things are true :lol:

    But when there is skew, the mode is not equal to the median, which is not equal to the mean.

    But you are right
    Offline

    2
    ReputationRep:
    (Original post by themathgeek)
    hardest s2 papers please? X

    posted from tsr mobile
    june 14 r
    Offline

    1
    ReputationRep:
    Could someone please help me with 5d on the June 2015 paper, thank you
    https://57a324a1a586c5508d2813730734...%20Edexcel.pdf
    (d) find the probability that the residents do not pay more than £500 to Liftsforall in thenext year.
    Attached Images
     
    Offline

    2
    ReputationRep:
    For anyone struggling to remember skews in a pdf use:

    PMQU

    P - M < Q < U

    Positive - mode < Quartile 2 (median) < mu (mean)

    and for a negative skew its the opposite direction
    Offline

    2
    ReputationRep:
    https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

    6c. Why have they used normal distribution?
    Offline

    1
    ReputationRep:
    Any thoughts on tomorrow's paper? - Hopefully it's going to be a 6 Question paper ending on a nice easy mean or median sampling distribution
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Has a teacher ever helped you cheat?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Write a reply...
    Reply
    Hide
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.