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Edexcel S2 - 27th June 2016 AM

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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?
i got k=1/18 but show b=8 and i got a =-12 help
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
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?
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
What are people thinking for boundaries? Lower than last year? About the same?
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
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
How did you find k for Q4? I proved b = 8.
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!
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
This is so depressing, needed to do well in S2 to get an A, probably got a B now.
(edited 7 years ago)
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?
Also does anyone have the exact working for K? I got 2/3 for some reason 😁
q4 funtion anyone
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.
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
Original post by kingaaran
What are people thinking for boundaries? Lower than last year? About the same?


that 8 mark approximation question will rocket the grade boundaries down.
Original post by RGBlinkFrayXx
Also does anyone have the exact working for K? I got 2/3 for some reason 😁


For K, you had to use the fact that you know that F( something ) = 1, and that F( something else )= 0 - I can't remember what the values were exactly but it was whatever the upper and lower bounds were ?

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