# How was Edexcel S2?Watch

This discussion is closed.
14 years ago
#121
(Original post by clare_m)
my god, why do people make it sooo difficult, ure find the area of the rectangle so length of base x length of height....so (2.7 - -1) x 1/5 = 0.74
ITS OBVIOUS
...lets stop discussing it....
If u read more carefully then u shud notice that i was only correcting what Russiandude had said was the answer, i.e. 0.54 when it should have been 0.74.
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14 years ago
#122
Hmm not that I need this exam. I was fine on the first 6 questions, made a silly mistake on the last question (when integrating, I didn't think to chuck in a +c, which apparently there was).
Oh well, thank goodness for ECF right? I still got negative skewness, they can't mark all the questions wrong, they have to ECF it, thankfully.
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14 years ago
#123
i did realise that, but it just confuses people when things are over-complicated. if people are stressed, just lay it out straight and they know if their right or wrong, and wont kid themselves that they might be right! soz if i offended, just wanted to clarify, which was why i used your quote, rather that ignoring what u said and making out i was some master of maths!!
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14 years ago
#124
so what grades do you people need? which uni's you going to? and which courses? i actually only need BBC for a business economics course at exeter but im striving for my A's, anyway!!
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14 years ago
#125
yea i see ur point, the way i explained it was a bit wierd....

yea ur way is beta...
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14 years ago
#126
I know I messed up the last question for sure since I forgot to include the 1/3 part. They had to be so evil and make it all fancy. I would have prefered a straightforward p.d.f question where you simply worked out the mean, variance, c.d.f, median, lower and upper quartiles and the IQR. I know how to do all them so despite not having included the 1/3 thing, I hope I can get some method marks. My lower quartile and median seemed a bit higher than what I have been hearing and my upper quartile was over the upper limit. For the skewness question, I went ahead and drew a box-plot! I suggested that it had a negative skew......

I doubt I will get an A in Maths now to go to King's College for Maths. I'm just hoping for a B, even if it's a crap one so that I still have a good chance at clearing. I got 65 on P2 and did find the P3 paper quite hard but I hope that I have got at least a B on the S2 paper with As in my S1 and P1 resits. I also got a B in my D1 last year. At the moment, I think I'm still on target for ABB.
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14 years ago
#127
(Original post by DaKe)
yea i see ur point, the way i explained it was a bit wierd....

yea ur way is beta...
well....i didnt wanna say that, but yes my way IS better, hee hee. its a girl thing!
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14 years ago
#128
wow a box plot, extravogent. i just used the mean<median<mode thing. tho had loads of time to spare, i did consider drawing the examiner a picture to be nice as i finished in 20 minutes. but decided it would be time better spent looking at the floor or ceiling. i should have done a box plot, i could have coloured it and everything, damn!
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14 years ago
#129
(Original post by clare_m)
wow a box plot, extravogent. i just used the mean<median<mode thing. tho had loads of time to spare, i did consider drawing the examiner a picture to be nice as i finished in 20 minutes. but decided it would be time better spent looking at the floor or ceiling. i should have done a box plot, i could have coloured it and everything, damn!
Well, I remembered that you could use the mean<median<mode thing but I didn't know which way round it was and plus, I would have had no idea of working out the mode, because I have hardly done any questions involving modes in continuous random variables. I also had like 40 minutes to spare as well and went over the paper a few times. I did change one answer though, the 7 marker involving the hypothesis test because of the word 'underestimate'. I didn't exactly know what the H1 was (and please don't tell me, I don't wanna know now!), so I changed it around! Oh well, as long as I get a B....

Btw, for the question where you had to explain what the critical region was or something, did you have to draw a diagram? Because I did and fully labelled it like 'if value appears here, H0 is rejected blah blah blah...'.
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14 years ago
#130
I got the same mean and median. Mean of about 1.27 and median of about 1.47. And I put it was negative skew, because it's always negative skew if median>mean as that means that most of the information is towards the right hand side of the graph.

I completley mucked up q3. I forgot how to do hypothesis test for binomial. Really stupid as that's the easiest one to do. I'll at least get method marks, I hope.
DO you think I will as the methods right, but I've put in one wrong number?
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14 years ago
#131
For question 6), the one with the carpet, on part d) how come everybody's got the normal approx to be Y~N(17.5,17.5). Me and my friends at school did the approx with lambda as 17.75 since 0.05*355 = 17.75
Is that right?
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14 years ago
#132
(Original post by davedave)
For the questions where you had X~B(100,0.1) and you were supposed to approximate it to find P(X > 15) or something, should it have been approximated as normal or poisson?

I thought you could do poisson as "n is large and p is small"
or you could do normal as np > 5 and n(1-p) > 5

so which should've been used? or would either have been ok?
Generally, when n is large and p is small, use the Poisson distribution to approximate a binomial distribution.

You are right that since n is large and np and nq are both >5, then a normal distribution is possible. But some books suggest that p should be close to 0.5, which is why I think that Poisson is preferred. However, I suspect that the examiner shaped the numbers so that both were possible.

John
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14 years ago
#133
PHP Code:
``` Did you all put (c.c) during normal approximation?  ```
Yeah u had to i think but its prob only worth a mark. My main worry for the exam was the prob functions bit but it turned out to be ok. Just hope i don't lose any marks on the hypothesis tests. I know this is a weird question but how did u define a sampling frame - just a list of sampling units
I wrote something like "A list of the data items in a population, such as a school roll."

John
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14 years ago
#134
(Original post by John Porcella)
I wrote something like "A list of the data items in a population, such as a school roll."

John
If you used the word list then you are guaranteed the mark for that question I think.
14 years ago
#135
(Original post by RussianDude)
do "trials" mean the same as "events"? Cos for binomial conditions i said that there must be a fixed number of events, not trials
I wondered that.

I think that they are different.

With Binomial, we tend to think of trials, such as the tossing of a coin. With Poisson, it seems to me to be more geared towards the rate at which an event occurs, e.g. three telephone calls every five minutes.

John
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14 years ago
#136
(Original post by Hingy)
For question 6), the one with the carpet, on part d) how come everybody's got the normal approx to be Y~N(17.5,17.5). Me and my friends at school did the approx with lambda as 17.75 since 0.05*355 = 17.75
Is that right?
17.75 is what I got too!

John
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#137
(Original post by John Porcella)
17.75 is what I got too!

John
me too
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14 years ago
#138
(Original post by John Porcella)
17.75 is what I got too!

John
But the question was something like P(x>15) and lamda is not tabulated for lamda = 17.75, so are you saying you did a 15 unit long expansion of poission?
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14 years ago
#139
But the question was something like P(x>15) and lamda is not tabulated for lamda = 17.75, so are you saying you did a 15 unit long expansion of poission?
Guessing that 17.75 was the value he (s)he used for the Normal.

i.e. (15.5-17.75_/(sqrt17.75) = P(z>0.89) <----Based on memery so it could be incorrect but I seem to remember doing something like that.
14 years ago
#140
Yes, it was the normal approx that I used. Approximating to Poisson didn't occur to me at all. But hopefully both methods should be ok
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