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Edexcel S2 - 27th June 2016 AM Watch

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    (Original post by SeanFM)
    a. b = 23/6

    b. k = 2

    c E(X) = 1.39. E(X^2) = 2.70. Var(X) = 0.77. Deviation = 0.88 (answers within that range, depending on rounding etc)

    d. IQR question removed - takes too much time.

    e. 0.69.






    Well done the last bit should be 2 s.f but doesn't matter really. Just something to be wary of in the exam if they specify how many s.f you need.
    (Original post by iMacJack)
    k=2 I got
    Well done
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    (Original post by SeanFM)
    a. b = 23/6

    b. k = 2

    c E(X) = 1.39. E(X^2) = 2.70. Var(X) = 0.77. Deviation = 0.88 (answers within that range, depending on rounding etc)

    d. IQR question removed - takes too much time.

    e. 0.69.






    Well done the last bit should be 2 s.f but doesn't matter really. Just something to be wary of in the exam if they specify how many s.f you need.
    hey man do you mind explaining the first part for me
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    (Original post by taysc)
    Attachment 556953

    Sean explained the first part to before. I thought I understood it but still managed to get the last part of the question wrong.

    I did 1 - (225)/(t+15)^2 = 0.1

    Can someone explain to me why its wrong. If you can make the explanation really simple, even child like. It would be really helpful
    This is the probability it survives for less than t days
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    (Original post by SeanFM)
    Not necessarily - I think it's just a method mark (hence the M) for having the 'right method'. The cao means 'correct answer only' so that's where the two methods will be differentiated - the one where it has been applied to the right one will get you that A1 mark.
    Ah alright I see, Ill just make sure to check the upper limits of each function and just work from there. Just wanted to clarify. Thank you!
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    This question
    6aii

    I don't understand why we are looking at the upper critical value and not the lower critical value as it says minimum

    Attachment 556929

    MS: Attachment 556931




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    June 15 (IAL) Q2b?
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    (Original post by NotNotBatman)
    Consider both sides of the rectangle:
    Look at the method used for question 11:

    http://www.madasmaths.com/archive/ma...stribution.pdf
    i still really don't get it
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    (Original post by Ben4)
    Do we need to know any proofs? I heard we need to know how to prove the variance of a uniform distribution... is this correct?
    Yeah you can be asked to work out the variance through integration (for uniform distribution) , which is basically the proof
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    I have a question about the S2 exam tomorrow, so I was doing past papers and some questions ask you to work E(X^2) for a CDF yet, solutions show the answer being gathered from the VAR(X) formula in the S2 formula booklet. Do you use the Var formula in the booklet for E(X^2) or am I nuts??
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    (Original post by ktbunny)
    I hope it is not too much trouble, but please could someone explain how they think through some questions to help my understanding!

    Attachment 556937
    1b)

    Attachment 556937556939
    2c)

    and

    Attachment 556937556939556900

    7d)

    Thank you very much in advance!


    Hope this helps mate!

    Appologies for hand writing.

    https://gyazo.com/af6ccadea92e33a2fa1cc2830439e94d
    https://gyazo.com/082b793a25a8162518a2bf5585ed8183
    Attached Images
      
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    (Original post by NotNotBatman)
    Consider both sides of the rectangle:
    Look at the method used for question 11:

    http://www.madasmaths.com/archive/ma...stribution.pdf
    is it because you don't know which side is the shorter side??? so it could be either which is why you add the probabilities for both??
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    (Original post by кяя)
    Is this the last A level exam in general? From the people I know S2 is last. 27th June is damn late... Can't believe how quick college flew by. Seems like yesterday I was going to open days.
    Along with FP3 it is one of the last A level maths exams, however I believe there is a physics exam the day after.
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    (Original post by XxNattyboyxX)
    hey man do you mind explaining the first part for me

    (Original post by SeanFM)
    A distribution X is used to model the length, in mm, of the first tear of a uPhone charger, and the PDF is specified below. However, Wapple have been careless and have lost some key details of the PDF.

    kx(1-x) if  0 \leq x < 0.5

    \frac{23}{40} - \frac{3x}{20} if    0.5 \leq x \leq b

    0 otherwise.

    a) Given that b is the minimum value greater than 0 such that f(b) = 0, find the value of b.

    So the b is the upper limit of the second part of the pdf. (f(x)).

    You are told that, after 0 (since f(0) = 0) b is the first value such that f(b) = 0.

    You automatically know that b is greater than 0.5, otherwise the pdf would not make sense, so you have to look at the second part and realise that the PDF in that part is a decreasing function, so there will come a point where f(x) = 0, and that x will be b. After f(x) is 0, you go past b, it doesn't become negative as you'd expect - it actually becomes 0, because after b, any x value falls into 'otherwise' so the graph flatlines. So you're looking for b, the y intercept.

    So that happens when
    \frac{23}{40} - \frac{3b}{20} = 0 \Rightarrow b = \frac{23}{6}

    Kind of hard to see to be honest. But don't worry, I don't think you'd get asked something like that, particularly in S2 - it's more like C3 stuff.
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    This year I did C3, C4, M1, S1, M1 and S2 tomorrow - is it fine to get my exams officer to place S2 in A2 Maths and keep AS FM all AS modules?
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    (Original post by Yasmin3101)
    I have a question about the S2 exam tomorrow, so I was doing past papers and some questions ask you to work E(X^2) for a CDF yet, solutions show the answer being gathered from the VAR(X) formula in the S2 formula booklet. Do you use the Var formula in the booklet for E(X^2) or am I nuts??
    Just like  Var(X) = E(X^2) - (E(X))^2 , you can rearrange that to give  E(X^2) = Var(X) + (E(X))^2 . which is useful especially if you know a formula for E(X) and Var(X) already. (eg for uniform distribution).
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    (Original post by Yasmin3101)
    I have a question about the S2 exam tomorrow, so I was doing past papers and some questions ask you to work E(X^2) for a CDF yet, solutions show the answer being gathered from the VAR(X) formula in the S2 formula booklet. Do you use the Var formula in the booklet for E(X^2) or am I nuts??

    E(X^2) Will be multiply all values in the PDF By X^2 before integration. Because the Var(X) Formula is multiply it by X^2 - x̄^2 think about how the equation works. Var(x) = E(X^2)-E(X)^2 Therefore to find E(X^2) You must only multiple all values by X^2 Then integrate.

    If asked form a CDF you must initally differentiate, then multiply by x^2 then go forward to integrate between b and a.
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    (Original post by SeanFM)
    So the b is the upper limit of the second part of the pdf. (f(x)).

    You are told that, after 0 (since f(0) = 0) b is the first value such that f(b) = 0.

    You automatically know that b is greater than 0.5, otherwise the pdf would not make sense, so you have to look at the second part and realise that the PDF in that part is a decreasing function, so there will come a point where f(x) = 0, and that x will be b. After f(x) is 0, you go past b, it doesn't become negative as you'd expect - it actually becomes 0, because after b, any x value falls into 'otherwise' so the graph flatlines. So you're looking for b, the y intercept.

    So that happens when
    \frac{23}{40} - \frac{3b}{20} = 0 \Rightarrow b = \frac{23}{6}

    Kind of hard to see to be honest. But don't worry, I don't think you'd get asked something like that, particularly in S2 - it's more like C3 stuff.
    ah thanks man, makes sense now
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    ]This question
    6aii

    I don't understand why we are looking at the upper critical value and not the lower critical value as it says minimum

    Attachment 556929

    MS: Attachment 556931






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    (Original post by AlphaArgonian)
    Along with FP3 it is one of the last A level maths exams, however I believe there is a physics exam the day after.
    Edexcel D2 is on Wednesday :'(
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    Hello Everyone,

    Hope revision is well

    Please could somebody help me in the June 2014 R paper question 5c
    https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

    How come they poisson to normal approximate rather than binomial to normal approximate because isnt binomial more accurate?
 
 
 
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