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Edexcel S2 Revision Thread

Haven't seen a thread made for S2 so I thought I would create one.

I have a question, on January 2008 question 5, Im a bit confused with the wording of the mark scheme, if the value lies in the critical region, then we reject Ho right? If you look in the mark scheme, it says "no evidence to Reject Ho" :s-smilie:

Where as you can clearly see in the mark scheme, the evidence which is 18 lies in the critical region of greate or equal to 18, can someone explain?

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Reply 1

diehardrocks

i think its just a printing error because if you look below its says the new fertilizer has 'increased' therefore implying that Ho is rejected. Hope that helps :smile:

Anyways how is your revision going ?

Reply 2

samir12

OP

16

Revision is going really good, I'm confident about S2 but I have a feeling they will give us a hard paper seeing as Jan 2010 paper was easy.

Reply 3

diehardrocks

samir12

Revision is going really good, I'm confident about S2 but I have a feeling they will give us a hard paper seeing as Jan 2010 paper was easy.

Cool. I also think that they might gives us a hard paper, but hopefully not :biggrin:

So what other modules are you taking this summer ?

Reply 4

samir12

OP

16

Im taking C4, FP2 and FP3, how about you?

Reply 5

diehardrocks

i'm taking FP2 and FP3

Reply 6

yeoni

Hey!
Could someone please help me with the question in January 2010 paper xD

SOLVED :biggrin:

Reply 7

samir12

OP

16

The question states that the critical region should be as close as to 0.005 as possible, so when finding the critical region for P(X≥C2)<0.005 it has to be as close to 0.005 as possible so when you translate it into 0.995<P(X≤C2-1), it has to be as close to 0.995 as possible, it doesnt matter if it is greater or less than 0.995, in the tabe the value x = 15 is the closest to 0.995 so C2-1= 15, therefore C2 = 16.

Reply 8

yeoni

samir12

The question states that the critical region should be as close as to 0.005 as possible, so when finding the critical region for P(X≥C2)<0.005 it has to be as close to 0.005 as possible so when you translate it into 0.995<P(X≤C2-1), it has to be as close to 0.995 as possible, it doesnt matter if it is greater or less than 0.995, in the tabe the value x = 15 is the closest to 0.995 so C2-1= 15, therefore C2 = 16.

SOLVED

Reply 9

laurenlodge

19

Ohhh S2. Kill me now.

Reply 10

felt_monkey

12

yeoni

Hey!
Could someone please help me with the question in January 2010 paper xD

6b) A discrete random variable X has a binomial distribution B(30,p). A single observation is used to test H0: p=0.3 against H1: p≠0.3
Sig level = 0.005 for each tail

P(X≤C1)+P(X≥C2)<0.01

P(X≤C1)<0.005
P(X≤2)=0.0021
0.0021<0.005
C1=2
X≤2

P(X≥C2)<0.005
1-P(X≤C2-1)<0.005
0.995<P(X≤C2-1)
P(X≤16)=0.9979
(1-0.9979)<0.005
C2-1=16
C2=17
X≥17

Answer says C2=16 instead :s-smilie:

where have I gone wrong? Thanks~ n__n

You haven't read the question properly. It says it must be as close as possible to 0.005, not smaller than 0.005. So look at the binomial table for (30, 0.3). 15 is closer to 0.995 than 16 is. Therefore it's C2 - 1 = 15, C2 = 16.

Edit: Sorry, didn't realise it had already been answered!

Reply 11

samir12

OP

16

yeoni

Thanks :] The S2 textbook makes it confusing, :confused:

I'm presuming you have the book, so like in example 13 (page 120) goes against what you are saying about the greater or less than not mattering:

X~(100,0.04) -> X~Po(4)
H0: p=4
H1: p>4
sig level=0.05%
P(X≥C)=1-P(X≤C-1)<0.05
0.95<P(X≤C-1)
P(X≤8)=0.9786
P(X≤7)=0.9489
Thus you are saying you should take P(X≤7)=0.9489 as it is closest to 0.95?
The book is saying that the critical region is X≥9 for 0.0214<0.05.

Sorry with my constant questions and if this sounds really dumb. xD

Because the question does not say "as close as possible to 5%" so it HAS to be less than 0.005. The greater or less than does not matter only if the question says "as close as possible to.." If it doesn't say anything about the critical region being as close as possible to whatever percentage, than it has to be less than. (or greater then if you are finding a critical region for p(x>c1)<0.05 which translates into p(x<c1) >0.95 so you find the first value greater than 0.95, not less than no matter how close it is)

Reply 12

yeoni

Thanks samir12, I get it now. :biggrin:

I will have to be more careful with reading the questions "closest".

Reply 13

pinkmojo

Hey guys,
When you have a question such as:
Find the probability that there were between 10 and 13 (inclusive) green mugs in this sample...
Do you just take it as 10>X≥13? How do you figure out which one is inclusive?
Thanks! =]

Reply 14

laurenlodge

19

pinkmojo

Hey guys,
When you have a question such as:
Find the probability that there were between 10 and 13 (inclusive) green mugs in this sample...
Do you just take it as 10>X≥13? How do you figure out which one is inclusive?
Thanks! =]

Inclusive means you include both 10 and 13 I think :smile:

Reply 15

TwilightKnight

11

Hypothesis teesssstttttiiingggg!!!!!!!!

My mortal enemy.

Reply 16

felt_monkey

12

TwilightKnight

Hypothesis teesssstttttiiingggg!!!!!!!!

My mortal enemy.

Mine are continuous uniform distribution (don't know why; I can do the simpler questions but not the harder ones) and CDFs and PDFs :sad:

Reply 17

laurenlodge

19

felt_monkey

Mine are continuous uniform distribution (don't know why; I can do the simpler questions but not the harder ones) and CDFs and PDFs :sad:

These things are APPALLING.

Reply 18

TwilightKnight

11

felt_monkey

Mine are continuous uniform distribution (don't know why; I can do the simpler questions but not the harder ones) and CDFs and PDFs :sad:

Heh, complete opposite for me. I found those by far the easiest chapters in the book, just because they make 'mathematical' sense if you get me. Im good at Calculus (not that you really NEED to be in fairness for CRV and CUD) and they're the first part of Statistics that has any sort of resemblance to the Core/ FP modules, so I just lapped them right up.

Im still sucking at hypothesis testing though. And I've only just managed with the help of a mnenomic to remember how to do continuity corrections with the Normal Approximations, lol.

Reply 19

felt_monkey

12

TwilightKnight

Heh, complete opposite for me. I found those by far the easiest chapters in the book, just because they make 'mathematical' sense if you get me. Im good at Calculus (not that you really NEED to be in fairness for CRV and CUD) and they're the first part of Statistics that has any sort of resemblance to the Core/ FP modules, so I just lapped them right up.

Im still sucking at hypothesis testing though. And I've only just managed with the help of a mnenomic to remember how to do continuity corrections with the Normal Approximations, lol.

Eurgh, I don't like S2 having anything to do with core :p:

. I love (love's the wrong word really...) Poisson, normal, binomial (as it's different to the C4 stuff!), hypothesis testing. If you're good with CDFs and PDFs, can I ask you something? If you have a CDF and there's a question for P(X<3) (for example) or P(X≤3), do you just do F(3)? And if it's P(X>4) or P(X≥4), is it 1 - F(4)?
The other thing - does anyone have a definitive list of definitions we have to learn? I.e. statistic, sampling frame, critical region etc. Thanks.

Edexcel S2 Revision Thread

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