S1 Jan 2012 Edexcel Post Exam Discussion Thread - Solutions in the first post Watch
Q1. Fairly easy histogram question (7)
Q2. Pretty tricky Venn diagram (9)
Q3. Standard DRV question (11)
Q4. Pretty easy/standard measures of location/spread question (11)
Q5. Pretty easy correlation/regression (issues with part f) (15)
Q6. Very easy Venn
Q7. Pretty simple normal distribution
I would expect fairly high boundaries for this paper
My guess would be
100UMS = 75
90 UMS = 70
80 UMS = 65
70 UMS = 58
60 UMS = 51
50 UMS = 45
40 UMS = 38
EDIT - This has been corrected on V2 of the solutions
EDIT - error on 4e)
I used the calculated mean and s.d. from earlier in the qu. For some reason, new values of the mean and s.d were given for part e)
scaled mean = 45
scaled sd = 9
(if you have made the same error, it is almost certainly 2 marks gone).
This question is very naughty.
From the calculations it would appear that the fake 5 year old coin weighing 20g is an outlier. Statistically, removing an outlier from a data set should increase the correlation between the two sets of data (It should make any formula generated more reliable).
So we would say PMCC increases, hence my solution.
However, given that the value of PMCC was -0.908, it would get closer to -1. So the value of the negative number should decrease. That said, you can understand why someone would say it is getting bigger, the negative number is getting bigger....
I have no idea how they will mark this one.
Furthermore, the data given is not possible. I appreciate it states 'without further calculation' but if you were to remove the fake coin, reduce your data set to 9 coins, calculate new values of Stt, Sww, Stw.
Stw changes to a positive value, meaning that there is now evidence of positive correlation, so PMCC WOULD INCREASE Numerically (if not statistically)
Sww is negative, which is impossible.
With such a small data set, 1 extreme piece of data will have a massive impact, so having an original PMCC so close to -1 doesn't make any sense in the first place.
If I am right, my raw marks would be around 73 (+/- 1).
for the pmcc increasing/decreasing question - if as time goes by, weirght decreases shouldn't the outlier mean there is a decrease in the PMCC and a stronger negative correlation?
I answered the Q just like arsey did, better get the marks !!!
Nah, it increases, 'cause if the correlation is closer to -1. meaning stronger correlation.. For that, it's only if the pmcc was positive, but it was negative, so decreasing pmcc means stronger correlation..