Ocr Mei S2

OP

Game_boy

The question, I believe, was 'what is the lowest mark someone in the top 10% could achieve'. Assuming integer, which I'm still not sure on, that mark would be the rounded up since the rounded down would not place you in the top 10%.

It's like, if you could get it the lowest mark would be 60.something, but since you can't the lowest you could is 61.

I know they've tested that concept in previous papers (not rounding by decimal extension, but looking for the lowest/highest value that still meets criterion X)

if that's the case then hopefully 61 is correct (assuming it's 61 and not 31 or 71 or something, lol).

I think you're also meant to use a continuity corection whilst finding it. But ahh God, who cares anymore.

Reply 22

Tallon

I think you're also meant to use a continuity corection whilst finding it. But ahh God, who cares anymore.

Possibly. They will only take max 1 mark for rounding it, wrongly/mistakenly whatever.

I'm more worried about follow-through on the regression line. They could give me everything, or worst-case take about 4 marks. I need 95%+ so I don't have to rely on getting 90+ in FP2 for an A*.

Reply 23

OP

Game_boy

Possibly. They will only take max 1 mark for rounding it, wrongly/mistakenly whatever.

I'm more worried about follow-through on the regression line. They could give me everything, or worst-case take about 4 marks. I need 95%+ so I don't have to rely on getting 90+ in FP2 for an A*.

I imagine you'll get a load of follow through marks. they only want to test if you can find a regession lnie once. after that they're testing if you can use it

indeed. FP2 is meant to be a bitch. I wonder how many marks spare you need for it to be safe? I have that and M2. Not sure how hard M2 is either.

Also, for the benefit of my friend who's asking me, what did you do for the question about the probability of getting a score of 111? I did P(110.5<x<111.5) using the new mean and SD they give you. Not entirely sure if that's right though.

Reply 24

Tallon

Also, for the benefit of my friend who's asking me, what did you do for the question about the probability of getting a score of 111? I did P(110.5<x<111.5) using the new mean and SD they give you. Not entirely sure if that's right though.

Yes, that's what I did. Except... new mean and s.d? Maybe I didn't read the question.

I did M2 last week. Liked it, nice exam. They can't throw ambiguous questions at you like stats can, so it's just whether you know the content.

For the A* they take your three best A2 modules, presumably including FP2. Since I did D2 last year (got 95) as well they could swap that in to exclude my weakest out of M2 and S2.

So if I got 95 on M2 (since I can't see what I got wrong) and assume S2 is worse then I'd need 80 on FP2 for an A*. Still hard, I really don't get the topics we've covered in FP2 to date (Matrices and Polar Coordinates).

Reply 25

OP

Game_boy

Yes, that's what I did. Except... new mean and s.d? Maybe I didn't read the question.

I did M2 last week. Liked it, nice exam. They can't throw ambiguous questions at you like stats can, so it's just whether you know the content.

For the A* they take your three best A2 modules, presumably including FP2. Since I did D2 last year (got 95) as well they could swap that in to exclude my weakest out of M2 and S2.

So if I got 95 on M2 (since I can't see what I got wrong) and assume S2 is worse then I'd need 80 on FP2 for an A*. Still hard, I really don't get the topics we've covered in FP2 to date (Matrices and Polar Coordinates).

I thought P(x=111) was the last part of Q3, where they were talking about UMS or unfirom scores from raw marks or whatever, right?

I know man. I've forgot all of FP2 and made room in my head for the 6 exams this month. You hear horror stories about how bad it is, lol. But I don't know if "bad" for people taking FP2 is a low A or a U or what, lol.

Reply 26

Tallon

I thought P(x=111) was the last part of Q3, where they were talking about UMS or unfirom scores from raw marks or whatever, right?

I know man. I've forgot all of FP2 and made room in my head for the 6 exams this month. You hear horror stories about how bad it is, lol. But I don't know if "bad" for people taking FP2 is a low A or a U or what, lol.

Probably. I'm not sure I used the new distribution, but I got something like 0.113 which sounds plausible.

Yeah, it's hard to tell with FP2 until we get there. I have far fewer exams in the summer (I have 7 this Jan) so I'll be able to concentrate, and if I try and get the A* I need in another subject then the mark I need in FP2 becomes low enough I don't need to worry. And, yes, part of its reputation is people taking FP2 thinking less than an 90% is a complete fail on their part. I'd include myself in that...

Reply 27

jamesBT

Game_boy

The question, I believe, was 'what is the lowest mark someone in the top 10% could achieve'. Assuming integer, which I'm still not sure on, that mark would be the rounded up since the rounded down would not place you in the top 10%.

It's like, if you could get it the lowest mark would be 60.something, but since you can't the lowest you could is 61.

I know they've tested that concept in previous papers (not rounding by decimal extension, but looking for the lowest/highest value that still meets criterion X)

The question was
"Find the least raw score which would be obtained by the highest scoring 10% of children." (I have the paper)
If you put 61 surely like 9.xx% of children would get the score not 10% as asked in the question. So I rounded down (or am I missing something?)
Meh. Its only Sadistics 2.

Reply 28

username219321

14

Tallon

ugh... you guys and your fancy calculators.....

Proper mathletes, right?

by the way, I'm pretty sure the question said the uniform score was rounded to the nearest integer? I'm sure it was 60 now, even though I forget the exact details of the question.

The finding score one didn't say anything about rounding I THINK, I may be wrong though :\

edit : yeah checked the paper from the post below and it just says least raw score, i.e. no rounding needed

Reply 29

OP

jamesBT

The question was
"Find the least raw score which would be obtained by the highest scoring 10% of children." (I have the paper)
If you put 61 surely like 9.xx% of children would get the score not 10% as asked in the question. So I rounded down (or am I missing something?)
Meh. Its only Sadistics 2.

then if you round down 10.xx% would get it, not 10%. Surely?
If you round up to 61, the highest 10% can get at least that score and be in the highest 10%
whereas if you round down to 60, a student could get that and not be in the highest 10%?

Not sure. Anyway, is the limit definitely 60.0 something if you have the paper right there? Cheers.

Also, is there a new mean and standad deviation for the P(x=111) question? Cheers.

Reply 30

Straightpath

8

jamesBT

The question was
"Find the least raw score which would be obtained by the highest scoring 10% of children." (I have the paper)
If you put 61 surely like 9.xx% of children would get the score not 10% as asked in the question. So I rounded down (or am I missing something?)
Meh. Its only Sadistics 2.

The answer has to be 61, as a student can only get either 60 or 61 in the test, and if they get 60 then thats not in the top 10%, 61 is.

Here's the paper:

Tallon

then if you round down 10.xx% would get it, not 10%. Surely?
If you round up to 61, the highest 10% can get at least that score and be in the highest 10%
whereas if you round down to 60, a student could get that and not be in the highest 10%?

Not sure. Anyway, is the limit definitely 60.0 something if you have the paper right there? Cheers.

Also, is there a new mean and standad deviation for the P(x=111) question? Cheers.

Yeah you're probably right, and for the other one the mean and s.d. are 100 and 15

Reply 32

Straightpath

The answer has to be 61, as a student can only get either 60 or 61 in the test, and if they get 60 then thats not in the top 10%, 61 is.

Here's the paper:

But what if the scores are continuous? Nowhere does it say the unadjusted score has to be an integer. I agree that if they are it's 61.

Tallon

Also, is there a new mean and standad deviation for the P(x=111) question? Cheers.

We can see from the paper that there is; I do think I used it.

Reply 33

OP

That Q(3) is so stupid.

Are the raw marks integers only or what?
because so for 3(i)A) when it wants P(x<50) does it actually want P(x<50) or P(x<49.5)?

Reply 34

username345307

14

Tallon

I imagine you'll get a load of follow through marks. they only want to test if you can find a regession lnie once. after that they're testing if you can use it

indeed. FP2 is meant to be a bitch. I wonder how many marks spare you need for it to be safe? I have that and M2. Not sure how hard M2 is either.

Also, for the benefit of my friend who's asking me, what did you do for the question about the probability of getting a score of 111? I did P(110.5<x<111.5) using the new mean and SD they give you. Not entirely sure if that's right though.

Yup, I did that! At first I was like 'wtf' when I read that question, came back to it and was fine about it.

I rounded to 60 for the other question though. *hangs head*

Reply 35

jakebv

yeah i had the same trouble in deciding whether to use continuity correction in the raw marks because surely they must be integers but then they asked something like P(43.5<X<50) so i think the raw marks were definetely continuous. So for the find the least raw...top 10% question i dnt think u needed to round it to the closest integer

Reply 36

Chriz M

I didn't round on the scores question, simply because it didn't say anywhere the score needed to be an integer, and the normal distribution is continuous. I was pleased with the lack of a full chi squared table, only needing to prove one point's contribution. Also was pleased there was a reasonably small amount of waffle questions, or wordy explanations, where I normally lose a few marks. Out of interested did everyone plot the data on graph paper? I was surprised they wanted us to do that.

Reply 37

OP

I think people did seeing as it was the first question.

I think you have to use continuity correctinos. It's a raw mark. You get raw marks for A level papers. You can only get whole number marks. Hmmm, I wonder.

Also P(x<50) was worth 3 marks??? Would it be if it was just P(x<50)?

Reply 38

Chriz M

Tallon

I think people did seeing as it was the first question.

I think you have to use continuity correctinos. It's a raw mark. You get raw marks for A level papers. You can only get whole number marks. Hmmm, I wonder.

Also P(x<50) was worth 3 marks??? Would it be if it was just P(x<50)?

As I understood, you don't need a continuity correction unless you are approximating the binomial or poission, unless is says it is an interger marks. I didn't use one for that bit.

Reply 39

OP