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# Edexcel S2 Exam Paper January 2011 14/01/11 Watch

1. For question 2, what did you guys set H1 to be? I put that h1 > 0.2...but for the conclusion I just said that the teachers claim was wrong...because the probability of getting more than 4 right was so low....but now that I think about it, h0 should be right. Which was silly because I so much time to spare but I didn't want to spend ages thinking about that question. I did all the working and got (P (X > 4) Something like 0.12. Just the conclusion was messed up. How much marks do you reckon I might loose ? It was 6 marks in total btw..
2. (Original post by lawwainam)
state the distribution of f(x)!?
I missed that!
I just substitute the values of the y-intercept and the x-intercept, is it ok?
I think that fully specifying the p.d.f gives you 2 marks, one mark for giving the limits of the p.d.f. and another mark for saying it is 0 'otherwise'. Or it could be just one mark.
3. (Original post by lawwainam)
state the distribution of f(x)!?
I missed that!
I just substitute the values of the y-intercept and the x-intercept, is it ok?
It said to state the distribution of f(x) for all real values, so it's the usual state f(x) thing. ...it was 4 marks...so u might lose 1 mark or 2 I guess
4. (Original post by Spongy)
For that question, i integrated the f(x) between the limits 0 and 0.5 and showed that the area is equal to one because the area under a p.d.f curve has to equal to one. Then i specified the p.d.f. .
I suppose there's loads of ways of doing that one. But yours seems to be the most relevant way to tackle it. Now that i think about it
5. (Original post by snowflakesblues)
For question 2, what did you guys set H1 to be? I put that h1 > 0.2...but for the conclusion I just said that the teachers claim was wrong...because the probability of getting more than 4 right was so low....but now that I think about it, h0 should be right. Which was silly because I so much time to spare but I didn't want to spend ages thinking about that question. I did all the working and got (P (X > 4) Something like 0.12. Just the conclusion was messed up. How much marks do you reckon I might loose ?
I have the same working out as yourself, working out P(X=>4) getting and aanswer of 0.12....
Then i put down accept H0 so the teacher's claim is wrong and that the student was not guessing! IS THIS CORRECT?????????????????????
Having seen previous mark schemes -> you get one mark for correctly accepting or rejecting H0 and another mark for giving a statement which is in context.
6. (Original post by cazzy-joe)
Yeahh that one first I was blank too but then I thought of this.
X--U[-1,3]
it said something 40 observations find probability of at least 10 is negative so I found out P(X=negative)=P(X<0)=0-(-1)*1/4=0.25

Then Y--B(40,0.25) find P(Y>=10)
If that looks fine

And how about the multiple choice question where they said to do one-tailed test, did you do alternative hyp more than or less then?? I got confused on that question I did more then (p>0.2) and X=4 dint fall in critical region so I wrote "Teacher's claim is WRONG".
I don't remember the hypothesis one but i think i did the same as you for the first one
7. (Original post by Spongy)
I have the same working out as yourself, working out P(X=>4) getting and aanswer of 0.12....
Then i put down accept H0 so the teacher's claim is wrong and that the student was not guessing! IS THIS CORRECT?????????????????????
Having seen previous mark schemes -> you get one mark for correctly accepting or rejecting H0 and another mark for giving a statement which is in context.
that's what I said, which was super silly. The teacher can only be wrong is P (X > 4) Is less than 0.05 (5 Sig level). I guess because 0.12 was such a low probability in my mind, I automatically assumed that the teacher was wrong. So Silly! But..the question was also worded really funny.....hopefully the grade boundaries will be low...
8. (Original post by warkan)
In that lambda question did u reject H0 because there was sufficient evidence??

and last question yeah i got 4.8 also i think... and the probably of it being less than 5 or smtin ? i got 4 numbers on both denominator and numerator..smtin like 2345/3456

and for the last one did u find 1-(p(x=0)+p(x=1)) ?
YEH i got 4 numbers on the denominator and numerator, although i know the top number was 6 thousand and something.. like 6240/5384 (but not that). I really thought it was wrong though because of how much of a not nice number it was! And yeh i think i found 1-(p(x=0)+p(x=1)) for the last one
9. (Original post by snowflakesblues)
For question 2, what did you guys set H1 to be? I put that h1 > 0.2...but for the conclusion I just said that the teachers claim was wrong...because the probability of getting more than 4 right was so low....but now that I think about it, h0 should be right. Which was silly because I so much time to spare but I didn't want to spend ages thinking about that question. I did all the working and got (P (X > 4) Something like 0.12. Just the conclusion was messed up. How much marks do you reckon I might loose ? It was 6 marks in total btw..
I think you will lose 2 marks
the method mark for using the probability
the answer mark for the contextual statement.
10. (Original post by lawwainam)
I think you will lose 2 marks
the method mark for using the probability
the answer mark for the contextual statement.
The method mark should be right...I think? Cause I got all the probabilities, just the conclusion bit was wrong. So statement mark is 1 mark? because I wrote not significant, accept h0, the teachers claim of the student guessing is "wrong" <-----this I wrote that as the last sentence of the paragraph....I hope the examiner stops after reading accept h0 ....hehe:P lol jk
11. (Original post by Kooper)
It usually is, but the null hypothesis has to be a fixed probability, and if the student isn't guessing, it isn't fixed - they could get anything between 1 and 10 out of 10. So we have to use the probability of getting it right by guessing (0.2) as it is the only fixed one available. The 4 out of 10 is only the result of 1 trial, it can't be turned into a probability.

So
H0 : p=0.2
H1 : p>0.2 (they're more likely to get it right if they aren't guessing)

At least I think that's right.

^Sorry if it doesn't make sense, it's a weird question and hard to explain!
Normally I would've done that, but the wording of the question made me question it a little so I ended up with:

H0: p>0.2
H1: p=0.2

Now obviously the rest of the method is the same, as is the probability at the end so that means I got the opposite conclusion? =[
12. (Original post by warkan)
Where can i find the S1 mark scheme?
13. Did everyone put down the assumption statements in context:
so the binomial one was related to the disease
and the Poisson one was related to cars arriving at the toll booth.
14. (Original post by snowflakesblues)
The method mark should be right...I think? Cause I got all the probabilities, just the conclusion bit was wrong. So statement mark is 1 mark?
According to the 2010 June Mark Scheme. There was 1 method mark for reject/accept.
But you find out all the probabilities, it should be fine
15. Nooooo I think I lost 1 mark for question 2 as I accepted h0 and then said that meant that the teachers claim was not correct as I thought the teachers claim was H1 how many marks you guys reckon lost there? 1 mark ?
16. (Original post by snowflakesblues)
The method mark should be right...I think? Cause I got all the probabilities, just the conclusion bit was wrong. So statement mark is 1 mark? because I wrote not significant, accept h0, the teachers claim of the student guessing is "wrong" <-----this I wrote that as the last sentence of the paragraph....I hope the examiner stops after reading accept h0 ....hehe:P lol jk
Then you should only loss 1 mark
17. So was the student guessing or not guessing !!!

Are we all agreed that we had to accept H0 which is p=0.2
18. (Original post by jit987)
As far as I remember my answers were: In any random order

M=15

Teacher question about guessing accept Ho because it was around 0.12..>0.05 so teacher claim was correct.

Question about ferry was reject Ho, because it was around 0.04..<0.05 so the ferry had improved in how late it was.

Positive skewness as Mean>Median>Mode...I calculated Mean to make sure which was 1/6..>Median(0.146...)> Mode(0)

Got some fraction like 3145/6561 for some answer. Then used that answer for the next part as Binomial (3 , 3145/6561) and did 1 - P(X=0)+P(X=1) using the formula.

Approximating the Poisson as Normal got P(Z< -2.1), then 1- P(Z< 2.1).

Finished the paper in 55 minutes but left the 5 marks uniform question out. Got confused with that question and even with 35 minutes to spare couldn't get the right method of (40, 0.25). I did another method of drawing the sketch with interval [-40 ,120]. P(X>=10) equalled the negative part of the graph and by doing this got answer of 3/4.(which sounded reasonable so left it with that) But after coming out of the exam lots of people did (40,0.25)...so lost the marks, any know if I will get 1/2 method marks?

Can't remember other answers...Someone at least post the QP or MS??????????
Agreed with most things you say, although I'm confused with the teacher one.. Surely if 0.12>0.05 you don't reject hypothesis because it's insufficient evidence? I thought it was only if it was within the critical region that you reject Everyone seems to be saying what you're saying though so i don't doubt you're right, just would like some explanation
19. For the second to last question the answer came out as a fraction "Like mentioned above", will I get penalized for rounding it to 4 s.f? I then followed up with the next question and used it binomially for the next one.....(last question was 3 marks btw) they don't take marks off for following through right??
20. (Original post by Spongy)
So was the student guessing or not guessing !!!

Are we all agreed that we had to accept H0 which is p=0.2
guessing i think

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