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# AQA Statistics 2 (B) Exam Thursday 21st June

Maths exam discussion - share revision tips in preparation for GCSE, A Level and other maths exams and discuss how they went afterwards.

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1. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by PhysicsGirl)
Hey, I don't know if this is helpful or not, but I always get confused as to whether to use n, or n-1, and I found this guide that the exam board publish as to which to use; http://store.aqa.org.uk/qual/pdf/AQA...1-GUIDANCE.PDF
Might be worth a look
I just looked at it and it didn't make that much sence, the way I understand it is for sample variance divide by n-1 and for the variance divide by n...
Is this correct?
2. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by Miyata)
Can someone please explain 6c) june 2011? http://store.aqa.org.uk/qual/gce/pdf...W-QP-JUN11.PDF can't do it, don't understand what they even want. Everything was going so well, but 6c... -6 marks, and last question, -7 marks, ran out of time so and messed up...
For 6c You know the top half equation of the cumulative distribution is 0.5, therefor integrate the other equation between q and 1 and make it equal to 0.25... Simplify and you will end up with a quadratic, solve and one of your results will lie outside the inequality so it has to be the other.
3. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by 5elsste)
For 6c You know the top half equation of the cumulative distribution is 0.5, therefor integrate the other equation between q and 1 and make it equal to 0.25... Simplify and you will end up with a quadratic, solve and one of your results will lie outside the inequality so it has to be the other.
Sorry, my mistake I meant 4c) both parts i) and ii). I managed to do 6c, but not d), I am thinking about d, almost understood it, but I am concerned about 4c I don't get it at all. Sorry again, hopefully you could explain 4c to me.
4. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by 5elsste)
I just looked at it and it didn't make that much sence, the way I understand it is for sample variance divide by n-1 and for the variance divide by n...
Is this correct?
Essentially, yes But it was saying that if asked for sample variance, you're allowed to be credited for using either, whereas if you're asked for an unbiased estimator of sample variance, you're have to use n-1, and that if you had to use sample variance indirectly (for example as part of a hypothesis test), you need to use n-1, but would receive full marks for using n iff n>30.
5. Re: AQA Statistics 2 (B) Exam Thursday 21st June
Hey, could someone please explain how to do stuff for continuous distribution, E(X), Var(X), median, quartiles etc and rectangular distribution. I'm not understanding anything the book is saying. Thank you =)
6. Re: AQA Statistics 2 (B) Exam Thursday 21st June
Anyone can help me here?

For the hypothesis testing, I can do the maths..etc but why do you accept the conditions (let's say H0) and reject the other?!

The only thing which I can't do atm!

Muchos gracias
7. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by ailish3park)
Hey, could someone please explain how to do stuff for continuous distribution, E(X), Var(X), median, quartiles etc and rectangular distribution. I'm not understanding anything the book is saying. Thank you =)

For the continuous distribution you have to integrate the function given!

Let's say the question says

f(x) = 1/3 2<x<4

To find E(X), you have to integrate 1/3 multiplied by x between the limits of 2 and 4; does that makes sense?

For Var(X), remember it is E(x^2) - E(x)^2 and work out your answer from there!

(for E(x^2) -basically integrate 1/3 multiplied by x^2 [as it is E(x^2)])

Does this makes sense?!
8. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by OnimushaGTA)
Anyone can help me here?

For the hypothesis testing, I can do the maths..etc but why do you accept the conditions (let's say H0) and reject the other?!

The only thing which I can't do atm!

Muchos gracias
You reject the null if the value you get exceeds the critical value
9. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by Lollyage)
Why didn't I take Decision 1 this year?

have a group snug to comfort you...I need one too really!
10. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by ailish3park)
Hey, could someone please explain how to do stuff for continuous distribution, E(X), Var(X), median, quartiles etc and rectangular distribution. I'm not understanding anything the book is saying. Thank you =)
Median, you should know from S1 that this is the middle number?
Quartiles - lower quartile 25% so 0.25; upper quartile 75% so 0.75 and so on!

Rectangular distribution is best illustrated by this (think of continuous random variables):

f(x) = 1/b-a a<x<b

To work out the mean it is 1/2(a+b) and the variance is 1/12(b-a)^2

Apart from these differences, it works similarly as a continuous distribution model; thus integration..etc! (could show you a proof but v. long + not required)
Last edited by OnimushaGTA; 20-06-2012 at 21:58. Reason: Missed out a word
11. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by OnimushaGTA)
For the continuous distribution you have to integrate the function given!

Let's say the question says

f(x) = 1/3 2<x<4

To find E(X), you have to integrate 1/3 multiplied by x between the limits of 2 and 4; does that makes sense?

For Var(X), remember it is E(x^2) - E(x)^2 and work out your answer from there!

(for E(x^2) -basically integrate 1/3 multiplied by x^2 [as it is E(x^2)])

Does this makes sense?!
Yeah kind of, thank you!
12. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by Lollyage)
You reject the null if the value you get exceeds the critical value
LALITA!

Haha! Sometimes that's not always the case though? I think
Some questions I did, where the value does not exceed the critical value and it was rejected!

13. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by Nerdatious)

have a group snug to comfort you...I need one too really!
Aww Massive snug is due after exams

(Original post by OnimushaGTA)
LALITA!

Haha! Sometimes that's not always the case though? I think
Some questions I did, where the value does not exceed the critical value and it was rejected!

NILESH!
It gets kinda confusing sometimes with negative numbers, so you have to be extra careful with those, but as far as I'm aware this rule always applies. Make sure you write the H0 and H1 correctly in the first place too, that's where I often screw up
14. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by Lollyage)
Aww Massive snug is due after exams

NILESH!
It gets kinda confusing sometimes with negative numbers, so you have to be extra careful with those, but as far as I'm aware this rule always applies. Make sure you write the H0 and H1 correctly in the first place too, that's where I often screw up
Okie dokes, need to do some more questions :P

(currently having roti and chicken curry )
15. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by ailish3park)
Yeah kind of, thank you!
Any more questions, quote me, I'm more than happy to help!
16. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by OnimushaGTA)
Okie dokes, need to do some more questions :P

(currently having roti and chicken curry )
Haha, funnily enough I'm having chicken curry tonight too

Comfort food before the dreaded S2
17. Re: AQA Statistics 2 (B) Exam Thursday 21st June
So I know that P(a⎪b) = P (a ∩ b) / P (b)
However in this question 4 cii (below) to my understanding - i may be wrong :L it does not this, to my understanding they are discrete random variables which they have done P (a) / P (b) as shown in the mark scheme
http://store.aqa.org.uk/qual/gce/pdf...W-QP-JAN11.PDF

Mark scheme:

http://store.aqa.org.uk/qual/gce/pdf...W-MS-JAN11.PDF

However for continuous random variables question 6d they have done :
P (a ∩ b) / P (b)

Why is this the case? Is P(a⎪b) for Discrete random variables P (a) / P (b) and for continuous P (a ∩ b) / P (b)? Please explain if i am wrong thanks
18. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by Lollyage)
Haha, funnily enough I'm having chicken curry tonight too

Comfort food before the dreaded S2

Haha, I can't wait for this time tomorrow!
I WILL BE FINISHED! YAYYYYY!

lol :P
19. Re: AQA Statistics 2 (B) Exam Thursday 21st June
So I know that P(a⎪b) = P (a ∩ b) / P (b)
However in this question 4 cii (below) to my understanding - i may be wrong :L it does not this, to my understanding they are discrete random variables which they have done P (a) / P (b) as shown in the mark scheme
http://store.aqa.org.uk/qual/gce/pdf...W-QP-JAN11.PDF

Mark scheme:

http://store.aqa.org.uk/qual/gce/pdf...W-MS-JAN11.PDF

However for continuous random variables question 6d they have done :
P (a ∩ b) / P (b)

Why is this the case? Is P(a⎪b) for Discrete random variables P (a) / P (b) and for continuous P (a ∩ b) / P (b)? Please explain if i am wrong thanks
20. Re: AQA Statistics 2 (B) Exam Thursday 21st June
(Original post by OnimushaGTA)
Haha, I can't wait for this time tomorrow!
I WILL BE FINISHED! YAYYYYY!

lol :P
SAAME!

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