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

1. (Original post by anshul95)
If I remember correctly I think the question said at least two. Could have said exactly two I don't remember.
I'm very sure it said atleast 2. So there are 2 ways of doing this:
1 - P(x+0)+P(x=1)
Or P(x+2)+P(x=3)

Also how did everyone explain how the f(x) is 4-8x from the diagram given.
I said because the f(x) is a straight line and a straight line is in the form y=ax+b, where b is the y-intercept and 'a' is the gradient(change in y/x). So y intercept is 4(from the sketch) and the 'a' is 4/0.5 = 8. Also because the slope is going from left to right it is representing negative gradient so -8. Therefore f(x) is -8x+4 (4-8x).
2. (Original post by anshul95)
Well if you reached the correct conclusion from your answers I think they have to at least give you one mark for method, maybe two if it says ft (follow through) on their mark scheme
ahh may not be too bad then, was the median worth 3 or 4 marks?
3. (Original post by mashman9)
Forgot to set my median to 0.5 so therefore got the skewness wrong to, anyone know how many marks the median and skewness were worth?!
3 and 1 respectively. You may, however, get the 1 mark skewness one as a follow through (error carried forward) if your reasoning was correct for the data you had found.

I found the exam very easy. I think, though, that the grade boundaries will go up to at least 63/75 for an A and who knows for an A*.

I remember the 4.8 as E(X) and the m=15 questions. For the rest, I just remember finding the second question (multiple choice test) very hard (my answer was 0.15 aprox, which I found strange as it was way over 0.05) and the rest of the paper straightforward.
4. (Original post by mathsphysics93)
3 and 1 respectively. You may, however, get the 1 mark skewness one as a follow through (error carried forward) if your reasoning was correct for the data you had found.

I found the exam very easy. I think, though, that the grade boundaries will go up to at least 63/75 for an A and who knows for an A*.

I remember the 4.8 as E(X) and the m=15 questions. For the rest, I just remember finding the second question (multiple choice test) very hard (my answer was 0.15 aprox, which I found strange as it was way over 0.05) and the rest of the paper straightforward.
ahh thanks, may have only dropped 3

Question 2 was odd, conclusion was she was guessing as H0 accepted, soo chance of getting a question right was 1 in 5,

Hopimg the boundaries dont go up!
5. I did each question twice to make sure I got a good mark as S2 grade boundaries are not funny. They're worse than D1. 65/75 for an A last year- WTF?!

Question 2 was odd and badly worded, infact I wrote a note to the marker saying that it was a terribly worded question. You can't do a hypothesis test to see if the probability of getting something right when there are 5 choices to be any different than 0.2! That's my opinion though.

Overall, the test was alright, they could have made a different question with E(X^2) (Question 3 I think). E(X) was 1, so anyone who forgot to square E(X) would get away with it :s . Good for us, but bad on their part.
6. What is the probability of the doctor will give injections?
I remember something like 0.08, right?
7. (Original post by chaz1992)
Overall, the test was alright, they could have made a different question with E(X^2) (Question 3 I think). E(X) was 1, so anyone who forgot to square E(X) would get away with it :s . Good for us, but bad on their part.
Yeah, I was thinking the same when working it out! I thought it was quite a "clever" question though, hadn't seen that type before
8. (Original post by lawwainam)
What is the probability of the doctor will give injections?
I remember something like 0.08, right?
yes that does seem familiar
9. I think it was a really good paper except Q2 which i (think) i got wrong!! I did:

H0 : p=0.2
H1 : p <.2

p(x<=4)

x~b(10,.2)
Looked up in the table....

got 0.96 something
0.96>0.05
so i accepted the h0.

How many marks will i get for this??Thanks
10. For the skewness question, I wrote the wrong thing!

I new it was positive, mode < median, but I wrote negative. Any chance I'd get a mark?
11. (Original post by Bleo)
okay so. Probability question 7 about with the tree diagram. The last one. Given that all three balls drawn out is of the same colour, calculate the probability that it is all red. How much marks was it, can anyone remember?

I would probably get it wrong. Is it independent of each other?
You're looking for S1

Here's the thread, with the question paper & (unofficial) mark scheme:

http://www.thestudentroom.co.uk/show...ussions_latest
12. (Original post by EnVogue)
For the skewness question, I wrote the wrong thing!

I new it was positive, mode < median, but I wrote negative. Any chance I'd get a mark?
hmmmm I doubt it because I have seen in some past papers saying no marks if you reach the wrong conclusion (for the exactly the same type of question)
13. (Original post by cpdavis)
I think it was a brilliant paper

First question: Quite easy (Binomial)

Second question: Once you get it, it was quite easy (the teacher's claim is correct meaning that she was guessing the answers. If she was guessing the questions, then the probability of her getting it right would have been more)

Third Question: The only tricky bit was the last question, but you had to use binomial distribution has you had a set number of trials and a probability of success of failure

Fourth Question: Quite easy

Fifth question: Basic C2 and the only bit I couldn't remember was the skewness, but then I realised it was positive

Sixth Question: I got m=15 (I think this was the ferry question)

Seventh Question: Was long, but I got all the aswers right. Although when I worked out P(x>5) I worked out F(x) and then solved it, even though there was a quicker way. But I still got the answer.

The last question, it was a binomial question, using the probability you used in the previous bit of the question

Overall I very good paper, I think it was be about 63/64 for an A
OMG, why you can remember that much!?
For the second question, I remember
H0: p=0.2 H1: p>0.2
Under H0, X~(10,0.2)
P(X>=4)=1-P(X<=3)
=1-0.8791=0.1209> 0.05
Therefore, the teacher claim is corrected. She is guessing.
For the last part of the third Question,
Something like
P(X<0)=1/4
Y~B(40,0.25)
Forget the followings
For the ferry question, I remember
H0:Lambda=8, H1:Lambda<8
P(X<=3)=0.0424< 0.05 too significant
Therefore, the services have improved.
For the car question,
I remember the last part is something like Y~N(25,25)
14. (Original post by lawwainam)
OMG, why you can remember that much!?
For the second question, I remember
H0: p=0.2 H1: p>0.2
Under H0, X~(10,0.2)
P(X>=4)=1-P(X<=3)
=1-0.8791=0.1209> 0.05
Therefore, the teacher claim is corrected. She is guessing.
For the last part of the third Question,
Something like
P(X<0)=1/4
Y~B(40,0.25)
Forget the followings
For the ferry question, I remember
H0:Lambda=8, H1:Lambda<8
P(X<=3)=0.0424< 0.05 too significant
Therefore, the services have improved.
For the car question,
I remember the last part is something like Y~N(25,25)
Overall I found the paper very good.

I agree with your answers above with one exception - the teacher's question. I worked out the same probability as you however I put down accept H0 therefore the teacher's claim is rejected because the result was not significant. ?!?!?

I have definately lost one mark because I got mixed up with the negative skew and positive skew.
15. (Original post by Spongy)
Overall I found the paper very good.

I agree with your answers above with one exception - the teacher's question. I worked out the same probability as you however I put down accept H0 therefore the teacher's claim is rejected because the result was not significant. ?!?!?

I have definately lost one mark because I got mixed up with the negative skew and positive skew.
I think it should be positive skew. I remember the mode is 0 and the median is something like 1.XX.
I think the teacher should be accepted since the probability>0.05 Am I right?
16. Okay for the question where it asked you to show that f(x) = 4 - 8x, did anyone just substitute the values in the range and show that they were similar to the graph? It was 4 marks, but it also asked you to state the distribution of f(x). So I thought 4 marks would be relevant for that. I did initially do the equation of a line (from C2) initially but crossed it out. Any chance i'd get the 4 marks ?
17. (Original post by lawwainam)
What is the probability of the doctor will give injections?
I remember something like 0.08, right?
i got something like that
18. (Original post by mashman9)
Forgot to set my median to 0.5 so therefore got the skewness wrong to, anyone know how many marks the median and skewness were worth?!
It was 1 mark.
19. (Original post by snowflakesblues)
Okay for the question where it asked you to show that f(x) = 4 - 8x, did anyone just substitute the values in the range and show that they were similar to the graph? It was 4 marks, but it also asked you to state the distribution of f(x). So I thought 4 marks would be relevant for that. I did initially do the equation of a line (from C2) initially but crossed it out. Any chance i'd get the 4 marks ?
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. .
20. (Original post by snowflakesblues)
Okay for the question where it asked you to show that f(x) = 4 - 8x, did anyone just substitute the values in the range and show that they were similar to the graph? It was 4 marks, but it also asked you to state the distribution of f(x). So I thought 4 marks would be relevant for that. I did initially do the equation of a line (from C2) initially but crossed it out. Any chance i'd get the 4 marks ?
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?

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