Hi guys
This is june 2013 (R)
for part a why is the mean a+2 and not 17.2
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Official Edexcel S3 thread Wednesday 20 May 2015 Morning [6691] watch
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physicshelper
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- 19-05-2015 11:00
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- 19-05-2015 11:04
(Original post by physicshelper)
Hi guys
This is june 2013 (R)
for part a why is the mean a+2 and not 17.2
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username1259045
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- 19-05-2015 11:05
btw i don't think we'll get tied ranks bc in the syllabus it says
"Regression and correlation
What students need to learn:
Spearman’s rank correlation coefficient, its use,interpretation and limitations.
Numerical questions involvingties will not be set. Someunderstanding of how to deal withties will be expected" -
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- 19-05-2015 11:07
(Original post by mmms95)
the mark scheme says anything from 2d.p or more is fine, but i usually do 3 d.p, might end up doing 4 d.p in the exam tho :P just in case -
physicshelper
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- 19-05-2015 11:16
(Original post by FN510)
You always use the population mean if you have it -
tggfootymad
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- 19-05-2015 12:34
There's no penalty for too many decimal places, so I always do it to 4 d.p.
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- 19-05-2015 12:36
Question 3 on the June 2012 paper
for part (d), the mark scheme states that 20k is above the upper confidence limit so the complaint is justified, could someone please explain this part to me? -
username1259045
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- 19-05-2015 12:40
(Original post by shamika)
P(|z|<3) = P(-3<z<3) always, by definition.
It is only 2 x P(z<3) if the distribution is symmetric about 0. Thus it is true for the standard normal, but won't be for a uniform distribution between 0 and 1 say.
(Original post by FN510)
Yeah, the diagram does help. If it p(|W| > 2) say, that = 2p(W >2). But if it was p(|W| < 2) that's equal to p(-2 < W < 2) -
getback339
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- 19-05-2015 12:47
(Original post by JuliM)
Question 3 on the June 2012 paper
for part (d), the mark scheme states that 20k is above the upper confidence limit so the complaint is justified, could someone please explain this part to me? -
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- 19-05-2015 12:51
(Original post by getback339)
20k is above the 95% certainty of mean time of car tyre change, therfore they are changing the tyres too soon -
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- 19-05-2015 12:54
I'm a little confused as to how much they expect us to know about proving biased/unbiased-ness in estimators...
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getback339
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- 19-05-2015 13:05
(Original post by JuliM)
So are they supposed to change the tyres if the mean lies within the confidence interval? This might be going over my head but I'm struggling to understand the question -
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- 19-05-2015 13:08
(Original post by getback339)
i didnt explain that very well to be fair... you worked out how many miles on average the garage replaces the brake pads. The actual number of miles before brake pads need replacing is 20,000 so the garage on average is changing them too soon. Im pretty bad at explaing haha -
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- 19-05-2015 13:54
(Original post by mmms95)
ahh okay, so just to clarify, its ALWAYS going to be 2 x probability it its normal distribution right? -
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- 19-05-2015 14:25
These high grade boundaries coupled with either one dodgy question or a couple of silly errors (like arithmetic errors) is making that A* very annoying
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nayilgervinho
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- 19-05-2015 14:34
For goodness of fit, hypothesis tests, how would we know when it's asking for a discrete uniform distribution?
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getback339
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- 19-05-2015 14:42
(Original post by nayilgervinho)
For goodness of fit, hypothesis tests, how would we know when it's asking for a discrete uniform distribution? -
nayilgervinho
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- 19-05-2015 14:44
(Original post by getback339)
it would be somthing obvious like fair coin or dice. -
getback339
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- 19-05-2015 14:49
(Original post by nayilgervinho)
So if the question mentions 'equally likely' I should assume it's a discrete uniform distribution. -
nayilgervinho
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- 19-05-2015 14:50
(Original post by getback339)
not necessarily, if the observed data looks the same for all values, you havnt found estimates for prob. etc... theyl make it clear for you
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