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# Edexcel S2 - 27th June 2016 AM

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1. (Original post by Karatekid Shiva)
Do we need to know the proofs for mean and variance: (a+b)/2 and 1/12(b-a)^12?? If so, how do u derive them?
Yes. Through integration - look on examsolutions

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2. 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.
3. 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

MS:

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4. (Original post by iMacJack)
Oh dear rookie error... thank you!

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Up to you whether you want to attempt the rest of the questions - the rest of the numbers don't come out so nicely but I'm getting some answers for it now.

(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.
S2 is pretty late, I think D2 and FP3 may be around the same time or later. (FP3 might clash with this, funnily enough).
5. (Original post by SeanFM)
I don't have the answers I'm afriad they may well not be fractions, it's the method that's most important anyway I'll have a look at the answers in a bit and quote you again.
Thank you!
6. (Original post by SeanFM)
Just in case there's 3 functions.. in general, as you'd expect, there's only 1 x value, or one of the functions, such that F(X) = 0.75, so equating to any one of them won't work - you first have to work out which one it actually is, usually by trial and error (and testing the ranges of each function, to use C3 lingo).
Oh alright I see, But also; I just looked at the mark scheme for the question I asked you about and it said this:
M1: putting their line 2 or their line 3= 0.75

.... Would you get the same answer then? I'm a bit confused now . My apologies
7. (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.
Nope. Other subjects left include Physic and other Maths modules such as AEA, M4, S4 (for AQA).
8. (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.

if

if

0 otherwise.

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

b) Hence find the value of k.

c) Find the expected length of the tear and the standard deviation.

d) Find the interquartile range of the length of tears.

e) Wapple send out an inspector to 5 random people who had asked for refunds. If the tear is longer than 1mm for at least 3 customers, all five will be refunded (ignoring systematic/human error). Find the probability, to 2 s.f, of Wapple giving a refund to a random group of 5 customers who have complained.
a) b=23/6
b)k=2
c)1.39 and 0.867
d)1.73
e)0.686

correct?
9. I hope it is not too much trouble, but please could someone explain how they think through some questions to help my understanding!

1b)

Attachment 556937556939
2c)

and

Attachment 556937556939556900
7d)

Thank you very much in advance!
Attached Images

10. (Original post by JammyW15)
Oh alright I see, But also; I just looked at the mark scheme for the question I asked you about and it said this:
M1: putting their line 2 or their line 3= 0.75

.... Would you get the same answer then? I'm a bit confused now . My apologies
You'd get a method mark for 'having the right idea'. (I haven't looked at the question properly so it could be that students either put the correct function on line 2 or line 3?
11. I was meant to self teach S2 today but i've lost the textbook .
12. Feel like this exam is going to be a bit of a disaster lol
13. (Original post by economicss)
Thank you!
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.

(Original post by LLk1)
a) b=23/6
b)k=2
c)1.39 and 0.867
d)1.73
e)0.686

correct?

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.
14. 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?
15. (Original post by SeanFM)
You'd get a method mark for 'having the right idea'. (I haven't looked at the question properly so it could be that students either put the correct function on line 2 or line 3?
I saw another question about finding the mean and equating F(m) = .5 and this is what the mark scheme says:

So doesn't that suggest either equation would get the same answer?
Attached Images

16. Can someone please explain 5(d)?

https://57a324a1a586c5508d2813730734...%20Edexcel.pdf
17. (Original post by JammyW15)
I saw another question about finding the mean and equating F(m) = .5 and this is what the mark scheme says:

So doesn't that suggest either equation would get the same answer?
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.

18. 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
19. I dont understand what they've done in june 14 (R) Q7d

https://57a324a1a586c5508d2813730734...%20Edexcel.pdf
20. (Original post by SeanFM)
Up to you whether you want to attempt the rest of the questions - the rest of the numbers don't come out so nicely but I'm getting some answers for it now.

S2 is pretty late, I think D2 and FP3 may be around the same time or later. (FP3 might clash with this, funnily enough).
k=2 I got

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