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Edexcel S2 - 27th June 2016 AM watch

• View Poll Results: How did you find the Edexcel S2 exam?
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1. (Original post by Bloom77)
Yep
The last question was particularly difficult
Not sure why the grade boundaries were quite high

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It was 58 for an which is isn't too bad, if I came out of the exam I would cry.
Yh I couldn't get the last part of question 7.
2. (Original post by Bloom77)
How do you know the area of a triangle is 0.5 in this question?
For part C

Attachment 556817

Mark scheme
Attachment 556819

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As the mean = mode we know that it is symmetrical (i.e. the area is shared between the two halves of the f(x))
3. (Original post by Billsonbubbles)
No you don't but dont worry about it,

I think you need to work out the probabilities, but you do need to convert to Z values and look in the normal distribution table ?

If thats what you were asking.

But make sure you add a continuity correction in there , as you are approximating a discrete to a continuos random variable..

Enjoy and hope that helped

Will
Thanks

Also regarding normal approximation for a hypothesis test, say your testing whether there's a decrease (for example X=20). With your continuity correction you would do P(X<20.5) right? So if testing for an increase you would do P(x>19.5)?

What would you do if your just testing for a change in the value of X?

Thanks again
4. https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

Question 1? how do i do it
5. Dont worry fixed my problem
6. Its a continuous uniform distribution
7. (Original post by keres)
Its a continuous uniform distribution
yeah but i dont get why the mark scheme got -0.5 and 0.5
8. (Original post by imran_)
yeah but i dont get why the mark scheme got -0.5 and 0.5
If something was measured to the nearest cm then error is 0.5 cm each way

E.g.
I measured my height to be 155.4 cm. This is 155cm to the nearest cm. But if I was 154.7 cm this would also be 155 cm to nearest cm.

In fact, if I was any height between 154.5 cm to 155.5 cm then I would be 155cm to the nearest centimetre.

this is gcse upper and lower bounds x
9. (Original post by imran_)
yeah but i dont get why the mark scheme got -0.5 and 0.5
+or- half scale division? thats what i would have thought.
10. https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

guys how do you approach q3c.

I'm kind of confused about how you start it

https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

11. (Original post by iMacJack)
As the mean = mode we know that it is symmetrical (i.e. the area is shared between the two halves of the f(x))
Thank you!

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12. 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) 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.

Spoiler:
Show

(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.

13. (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 has been careless and have lost some key details of the PDF.

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.
I will do this question, however could you fix the latex pls?
14. (Original post by iMacJack)
I will do this question, however could you fix the latex pls?
Working on that as we speak. Shouldn't be too hard to read though.
15. Marking June 14 (r) and then I'll get onto that question SeanFM
16. 70/75 in June 14 (r)

Ok - now to Sean's q...
17. https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

how would I do question 4? idk where to start from

SeanFM
18. (Original post by imran_)
https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

how would I do question 4? idk where to start from

SeanFM
It's to do with the critical region, the % significance and what value of k is most suitable (see from tables, trial and error)
19. (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.
Is part a B = 23/6? I have a feeling I have done something wrong
20. Anybody know how to do 3b? It's from the june 2013 paper, I looked at exam solution but I still don't understand why you start off with p(x>n), how do we know that we should use it this way around?

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