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Ocr mei statistics 1 exam thread (24/05/13)

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Original post by Blobar
You needed to times the first answer by 3 at the end as there are 3 different ways of getting that.


Ah damn, I really wasn't sure. I should hopefully get 2 of the marks though. And maybe some method marks for part ii).
Reply 341
Avatar for Blobar
Blobar
15
Original post by jonny7bell
A few papers I have done on S1 have got to 53 as an A. A few have been rather high, but I think this will probably be around 55-57 for an A, as Q2 and the last question probably threw a few people off. So I would still say a mid B.


I'd say whoever gets 50 will be lucky to get a B, rarely do I see past papers which dip below 57 and some are even higher than that. There's always hard questions on the papers even where the grade boundaries are 57 so I think it will be about 57 +/- 1
Reply 342
Avatar for Mahinder
Mahinder
jonny bell i did 5/10 x 4/9 x 5/8 x 3! because theres 3 different ways they could have been picked
The last part of the last question was:

P( BULL AND BULL AND BULL) + P( MISS AND MISS AND MISS AND BULL AND BULL AND BULL)


:biggrin:



All in all, a really good exam i thought :smile:
Original post by lorobolorolo
I'm not completely sure, but I think question 3 was the question on the bag of flours which weighed 1.5kg or something like that. And then they asked u to calculate something about 50 bags and then there was the question about 20 in a box and whats the probabilty of at least 1 bag being underweight. Correct me if i'm wrong.


Yeah, question 3 was the binomial one.

"The weights of bags of a particular brand of flower are quoted as1.5kg. In fact, on average only 10 percentage of the bags are underweight"

i) Find the problem of exactly 5 bags out of 50 being underweight
ii_ Find the probability that at least 1 bag out of 20 is underweight
iii) A crate contains 48 boxes. Find the expected number of boxes in the crate which contain at least 1 underweight bag.
Reply 345
Avatar for Mahinder
Mahinder
u mean 3! not 3 blobar
Original post by Mahinder
jonny bell i did 5/10 x 4/9 x 5/8 x 3! because theres 3 different ways they could have been picked


Yeah that makes more sense, ffs.
Reply 347
Avatar for dada55
dada55
19
Original post by Blobar
I'd say whoever gets 50 will be lucky to get a B, rarely do I see past papers which dip below 57 and some are even higher than that. There's always hard questions on the papers even where the grade boundaries are 57 so I think it will be about 57 +/- 1


S1 papers are somewhat an exception, "speaking statistically, the median is around 56/57 for an A, however there have been a few outliers of around 53 for an A"

Sorry I had to do this.
Reply 348
Avatar for Moon1ight
Moon1ight
OP
15
Bricking it for what I get in maths now,Honestly if luck decided to enlighten me after all the hours I've put in in these exams,ill get my A with at A B C in the three exams , the worst is a D for me,never going to look at maths related threads on here because it just messes your mind up.Having said that I have to thank everyone who helped me on here and the mega a level maths thread.good luck everyone who has forthcoming exams.If only the amount of work you put into exams decided your grades eh ?


Posted from TSR Mobile
Did everybody find themselves rejecting the test on question 5? I got P(x<=13)=0.1316.0.05 so not enough evidence.
Original post by Mahinder
jonny bell i did 5/10 x 4/9 x 5/8 x 3! because theres 3 different ways they could have been picked


Sounds good, but you would just times by 3, not 3!

it was : ( 5/10 x 4/9 x 5/8 ) + ( 5/10 x 4/9 x 5/8) + ( 5/10 x 4/9 x 5/8 )

So basically just: 3 x ( 5/10 x 4/9 x 5/8 )

if you were to times it by 3! it would be: 6 x ( 5/10 x 4/9 x 5/8 ) [which is incorrect sorry sorry sorry ]
Reply 351
Avatar for juniorx
juniorx
2
Original post by jonny7bell
What did everybody do for question 2? That was the only question I found rather hard.

I did:

i) 5/10*4/9*5/8=5/36
ii) I tried to binomial distribute it and got 0.0096, no idea if it was right though.


can someone remind what this question was about???
Reply 352
Avatar for Mahinder
Mahinder
so for question 3 i did


x-b(50, 0.1)
p(x=5) = 50c5 x0.1^5 x 0.9^45

ii)
x-b(20,0.1)
p(x>=1)=1-p(x<=0) = 0.874

then it was expectation question i think so it was 48 x 0.874
also, critical region was X>=15


right?
Original post by Mahinder
so for question 3 i did


x-b(50, 0.1)
p(x=5) = 50c5 x0.1^5 x 0.9^45

ii)
x-b(20,0.1)
p(x>=1)=1-p(x<=0) = 0.874

then it was expectation question i think so it was 48 x 0.874


that's correct :smile:
Reply 355
Avatar for juniorx
juniorx
2
Original post by Mahinder
so for question 3 i did


x-b(50, 0.1)
p(x=5) = 50c5 x0.1^5 x 0.9^45

ii)
x-b(20,0.1)
p(x>=1)=1-p(x<=0) = 0.874

then it was expectation question i think so it was 48 x 0.874


**** do you lose marks for not writing this even if you get the answer?
Original post by Mahinder
so for question 3 i did


x-b(50, 0.1)
p(x=5) = 50c5 x0.1^5 x 0.9^45

ii)
x-b(20,0.1)
p(x>=1)=1-p(x<=0) = 0.874

then it was expectation question i think so it was 48 x 0.874


I got 0.8784 for ii), then 42.2 for iii).
But assuming you made a typo, that is what I got.
Original post by juniorx
**** do you lose marks for not writing this even if you get the answer?


probably about half
Reply 358
Avatar for Moon1ight
Moon1ight
OP
15
Did we all accept h0 for the hypothesis test ?


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Original post by tumblrgirl
me too, I did (5C2 x 5C1)/10C3 and i got 5/12 as my answer:s-smilie:
I did the same, There was wayyy too much probability in this paper

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