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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%

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    (Original post by Armpits)
    How did you work out k?
    If I recall, what I did was set F(2) equal to zero, and work from there. I might've also used F(3)=1
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    (Original post by Armpits)
    How did you work out k?
    F(2) = 0
    F(3) = 1

    simultaneous from there

    (Original post by Mathemagicien)
    I'm an idiot (and I have a headache), I completely forgot how to do q5 - I got Z=1.75, but I thought the variable X (number of students owning laptops) was binomial (n, 1/5), which was approximated by N(n/5, 4n/25)...

    then I said P(X>55) = P(2(root n)Z/5 + n/5 > 55.5) = P(Z>5[55.5-n/5]/2(root n) ) = P(Z=1.75)

    Could you be kind and tell me where have I gone [horribly, stupidly] wrong (or what I should have done)? Else I'm going to spend the whole summer trying to figure it out
    I did get that binomial and normal

    Bolded part I don't recognise

    i had something like (55.5 - 0.2n)/0.4sqrt(n) = 1.75
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    Guys, wasn't the E(X) question 53 pi? Because it's the E(X) of a normal distribution so b-a)/2? Where b=81 pi and a=25 pi?
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    i got k=1/18 but show b=8 and i got a =-12 help
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    judging by the poll distribution, i can guess the grade boundaries will be low.
    68 - A*
    62 - A
    54 - B
    48 - C
    42 - D
    36 - E
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    (Original post by Oxyfrost)
    If I recall, what I did was set F(2) equal to zero, and work from there. I might've also used F(3)=1
    Since the pdf was quadratic, I assumed median was 2.5 due to symmetricity, set the cdf = 0.5, and put x=2.5 in the eq. Then I attempted to solve simultaneously with integrated pdf = 1.

    Do you think I'll get method marks?
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    (Original post by RGBlinkFrayXx)
    Guys, wasn't the E(X) question 53 pi? Because it's the E(X) of a normal distribution so b-a)/2? Where b=81 pi and a=25 pi?
    no

    you're looking for pi*E(X^2) since E(A) = E(piR^2) = pi*E(R^2)

    Var(R) = E(R^2) - E(R)^2


    You can work out Var(R) and E(R) simply from the stuff in the formula book and work from there
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    What are people thinking for boundaries? Lower than last year? About the same?
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    How many marks do I lose

    I wrote 18k= 2 so k= 9 (loool I'm such an idiot)

    And for the 8 marker I did the normal distribution up to the quadratic where y=n^0.5 . So out of the 8 how many marks will I get

    Also grade boundary predictions?

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    (Original post by Mathemagicien)
    Wait, that looks like what I got

    I think I did something retarded like multiplying the LHS by root n instead of dividing it...

    :dunce:
    Your method was fine then. Should just be a couple of A1s lost
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    (Original post by RGBlinkFrayXx)
    Guys, wasn't the E(X) question 53 pi? Because it's the E(X) of a normal distribution so b-a)/2? Where b=81 pi and a=25 pi?
    I did this but we're probably wrong
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    How did you find k for Q4? I proved b = 8.
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    (Original post by AMarques)
    For 3b it should be (9-7)/(9-5) = 1/2 since R goes up to 9 and not 10. I think.
    That's right! Edexcel can be very sneaky, can't they? I'm just so glad that I managed to see it... I've made that same mistake many times before, and so I was really looking out for it this time!
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    (Original post by smartalan73)
    Anyone else check the front the paper after reading the first question to make sure it was S2 and not S1?
    I did lol
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    This is so depressing, needed to do well in S2 to get an A, probably got a B now.
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    Ah okay. So will there be any method marks for what we did? Or are they all gone? Does anyone know how many marks this was worth?
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    Also does anyone have the exact working for K? I got 2/3 for some reason 😁
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    q4 funtion anyone
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    (Original post by tiny hobbit)
    No but I would write down the
    x (squiggle) N or B or Po (distrubution)
    so that they know what you were intending to use in case you look up the wrong number.
    There is often a mark for "evidence of using ...... distribution".
    You don't gain marks for declaring variables, but you do get a mark for stating the distribution. And as the guy above says, declaring variables helps the examiner to follow what you're doing, which is good if your final answer isn't right.
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    Pretty sure you got 6 wrong, cos I think you have to square root the n on the bottom, making n quite a lot larger than 62, thats what I got as well but I'm pretty sure it's wrong
 
 
 
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