S1 Jan 2012 Edexcel Post Exam Discussion Thread - Solutions in the first post

Poll

Having seen the solutions, how many marks do you think you got?

Other than Q2 I thought this was quite an easy paper, marks seem quite generous too.

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).

Edit 5f)

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.

(edited 12 years ago)

12 Jan S1 Model V2 red.pdf856.6KB

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Reply 1

swagge

4 e) it asks for the mean of all the students which is given in the question, you seem to have done it for the calculated one?

Reply 2

Musical-Ocean

Original post by swagge

4 e) it asks for the mean of all the students which is given in the question, you seem to have done it for the calculated one?

lol, i made the same mistake !

Reply 3

Arsey

Original post by swagge

4 e) it asks for the mean of all the students which is given in the question, you seem to have done it for the calculated one?

missed that, it is a bit of an odd thing to put in the qu

in that case,

scaled mean = 45
scaled sd = 9

Reply 4

Webb04

Decent paper i thought actually :smile:

made up for a few silly mistakes in C2

Reply 5

IAmTheChosenOne

Original post by swagge

4 e) it asks for the mean of all the students which is given in the question, you seem to have done it for the calculated one?

So what would the answer be?

Thanks.

Reply 6

IAmTheChosenOne

Original post by Arsey

missed that, it is a bit of an odd thing to put in the qu

in that case,

scaled mean = 45
scaled sd = 9

For standard deviation, I divided by 0.9 :frown:

Reply 7

Legendary

Thanks for the solutions but you worked out the mean question wrong your meant to use 50 and 10 other than that 75/75 :biggrin:

D1 is next :colone:

Reply 8

larryay

I agree the paper this time was easier than normal.
If I am right, my raw marks would be around 73 (+/- 1).

Reply 9

POWW!

This has been harder for me then the other papers. :l Counted 65 :l

Reply 10

IAmTheChosenOne

Original post by POWW!

This has been harder for me then the other papers. :l Counted 65 :l

Same here. Weird :eek:

Hey everyone, was this paper really that easy?

I found it to be more difficult than past papers... :lolwut:

Reply 11

POWW!

Original post by IAmTheChosenOne

Same here. Weird :eek:

Hey everyone, was this paper really that easy?

I found it to be more difficult than past papers... :lolwut:

YES ! esp 1b lol sat there staring at it for 5mins

Reply 12

vishalb

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?

Reply 13

IAmTheChosenOne

Original post by vishalb

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?

This is what I put!

Reply 14

Fardip

Original post by vishalb

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?

LOL Vishal!! :smile:

Remember, the pmcc is negative, so decreasing means stronger correlation.. :smile:

Reply 15

vishalb

Original post by Fardip

LOL Vishal!! :smile:

Remember, the pmcc is negative, so decreasing means stronger correlation.. :smile:

I know! I agree with you. So doesn't that mean that the PMCC decreases rather than increases as written in the markscheme by Arsey?

Reply 16

Fardip

Original post by vishalb

I know! I agree with you. So doesn't that mean that the PMCC decreases rather than increases as written in the markscheme by Arsey?

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.. :biggrin:

Reply 17

IAmTheChosenOne

Original post by vishalb

I know! I agree with you. So doesn't that mean that the PMCC decreases rather than increases as written in the markscheme by Arsey?

Yeh! That's what I thought... isn't it?

Reply 18

Musical-Ocean

Original post by vishalb

I know! I agree with you. So doesn't that mean that the PMCC decreases rather than increases as written in the markscheme by Arsey?

Increases in the sense that the correlation increases, but decreases in the numerical sense.
I answered the Q just like arsey did, better get the marks !!!