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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%

1. (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
2. (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
3. 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?
4. i got k=1/18 but show b=8 and i got a =-12 help
5. 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
6. (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?
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
8. What are people thinking for boundaries? Lower than last year? About the same?
9. 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

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10. (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...

Your method was fine then. Should just be a couple of A1s lost
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
12. How did you find k for Q4? I proved b = 8.
13. (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!
14. (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
15. This is so depressing, needed to do well in S2 to get an A, probably got a B now.
16. 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?
17. Also does anyone have the exact working for K? I got 2/3 for some reason 😁
18. q4 funtion anyone
19. (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.
20. 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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