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# Edexcel S2 - 27th June 2016 AM

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1. (Original post by SeanFM)
2.37, I think you mean, and I would go for 2.37 (round to closest 2 d.p)
2.37 isn't in the table, it is 2.36 or 2.38
2. (Original post by SeanFM)
2.37, I think you mean, and I would go for 2.37 (round to closest 2 d.p)
oh hang on, would i round to 2.36 as 2.367 is closer to 2.36 than it is 2.38?
3. (Original post by tazza ma razza)
2.37 isn't in the table, it is 2.36 or 2.38
Oh, I apologise - haven't seen the tables in ages in that case, round to the closest one.
4. (Original post by SeanFM)
Oh, I apologise - haven't seen the tables in ages in that case, round to the closest one.
look at post 175 - is this what you mean
5. (Original post by tazza ma razza)
oh hang on, would i round to 2.36 as 2.367 is closer to 2.36 than it is 2.38?
Yes. (as far as I can remember, it makes more sense anyway)
6. (Original post by taysc)
I can set out what I do/format I use and take a picture.
I can do it in about an 45 mins to 1 hour if you don't mind? if you find two questions that will be helpful or I can do it with random letters and numbers?
Ahh thanks so much! heres one that i'm confused on atm (only part e) but idm if you use random letters and number
7. (Original post by Michaelj99)
Ahh thanks so much! heres one that i'm confused on atm (only part e) but idm if you use random letters and number
Seems like a standard hypothesis test?

So you've got a binomial with n = 50 and p = 0.25, you've got your H0: P = 0.25, and your H1: P < 0.25 (As it asks if it has decreased)

You then test P(X<=5) using binomial tables with 50, 0.25 and conclude?
8. (Original post by iMacJack)
Seems like a standard hypothesis test?

So you've got a binomial with n = 50 and p = 0.25, you've got your H0: P = 0.25, and your H1: P < 0.25 (As it asks if it has decreased)

You then test P(X<=5) using binomial tables with 50, 0.25 and conclude?
Oh so do you always test the evidence? i.e 5 and how would you know would it be less&= to? would it be because it's lower than the expected of 12.5?
9. (Original post by Michaelj99)
Oh so do you always test the evidence? i.e 5 and how would you know would it be less&= to? would it be because it's lower than the expected of 12.5?
I think the general consensus is to test in the direction of your alternate hypothesis

So we have H1 P<0.25, so we want to test if that result of 5 is significant, so we test <= to it.

This is what I do anyway - and I always seem to get them correct!
10. (Original post by Michaelj99)
Ahh thanks so much! heres one that i'm confused on atm (only part e) but idm if you use random letters and number

Hopefully it is clear enough. Hopefully it will help,if you need me to clarify anything or explain it more just say. (sorry about any spelling mistakes)

From what you've said above it seems your confused about whether to do an upper tail or lower tail. It says decrease hence lower tail, if it said increase I would use a upper tail.

Another way of thinking about it is if you have
X - B[20,0.2] and they actually got X=12 in their observation

E(X) = 20 x 0.2 = 10

(but they actually got X=12)

So it must mean you should test for an increase

H0 : p = 0.2
HI : p > 0.2
11. (Original post by taysc)

Hopefully it is clear enough. Hopefully it will help,if you need me to clarify anything or explain it more just say. (sorry about any spelling mistakes)

From what you've said above it seems your confused about whether to do an upper tail or lower tail. It says decrease hence lower tail, if it said increase I would use a upper tail.

Another way of thinking about it is if you have
X - B[20,0.2] and they actually got X=12 in their observation

E(X) = 20 x 0.2 = 10

(but they actually got X=12)

So it must mean you should test for an increase

H0 : p = 0.2
HI : p > 0.2
Ohhhh that makes sense thank you
12. hi guys i nearly always get the boundaries and the sign for the continuity correction wrong. do you guys have any trick or tip on how to do the boundaries bc they are easy marks im losing right now!

any help is much appreciated thankss!!
13. (Original post by Superbubbles)
Need help on 2015 paper q3b anyone know??
the mode question? Draw a sketch of the pdf graph and look for the highest point!
14. also to how many s.f or decimal places should we put our answers?
15. (Original post by alvosm)
hi guys i nearly always get the boundaries and the sign for the continuity correction wrong. do you guys have any trick or tip on how to do the boundaries bc they are easy marks im losing right now!

any help is much appreciated thankss!!
It takes practice (not necessarily of actual questions where you use a CC, just identifying what they would be given an inequality).

You can convert '<' and '>' into less than or equal to and greater than equal signs first, and then just apply the same logic to them, so trying to figure out what to do in 2 cases rather than 4, if you see what I mean.

So if I said, continuity correction - add 0.5 for x less than or equal to something, so that the values above the 'greatest' in the continuous distribution round down to the 'greatest' in the discrete distribution. (continuity correction is )

The other case is >.continuity correction - take away 0.5 for x greater than or equal to something, so that those values round up to the 'least in the discrete distribution.
(continuity correction is )

The other two cases are greater than or equal to and less than or equal to, but they're like the two ones above, just without the first step.
16. hardest s2 paper?
17. (Original post by kyungsoo)
the mode question? Draw a sketch of the pdf graph and look for the highest point!
Is this the only way ? It's only one mark
18. Zacken SeanFM Can either of you guys (Or anyone else) chuck me a random question to do? I am so bad at making myself do questions!! I will do any of the questions you reply to me with
19. (Original post by iMacJack)
Zacken SeanFM Can either of you guys (Or anyone else) chuck me a random question to do? I am so bad at making myself do questions!! I will do any of the questions you reply to me with
Can't promise anything but I'll look through past papers to see if there is anything interesting that can be made..

(you might want to try the madasmaths stats booklets too).
20. (Original post by Superbubbles)
Is this the only way ? It's only one mark
Haven't looked at the question but I imagine if it's one mark then it will be that method. That's usually the case when the function is linear, in which case it's clear which is the modal value. Otherwise, usually if its a quadratic or cubic, you can differentiate the function and find the turning point of it, which is usually the modal value.

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