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# Edexcel S1 - 15th June, 2016 [Exam Discussion] Watch

1. I think it was 4 marks 2 marks for each. 2 marks for explaining whats gonna happen to the mean and sd and two for explaining why

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2. (Original post by SelfishWeiner)
As you did previously for x, but using 1/x in its place with the same probabilities.

i did that 9 without X'ing the values but it dint add up to 1 so i just dived E(x) by 1 to give me E(r), how many marks do you think ??
3. (Original post by jasmine9876)
I think it was 4 marks 2 marks for each. 2 marks for explaining whats gonna happen to the mean and sd and two for explaining why

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No it was two marks, it was three marks for calculating the mean and Standard Deviation of the babies weights
4. (Original post by leestitt)
I found a short way, all you had to do was square the Standard deviation and multiply it by 8.
I found this way in the exam after equating SD to √(Σy^2/n - μ^2), solving for Σy^2 and subbing everything into Syy (which took about half a page, compared to the one line σ^2 x 8). I scribbled it down under the heading "Alternate method for part (b)", but I don't actually understand why it works. Is there some formula it's based on?
5. (Original post by ShatnersBassoon)
I found this way in the exam after equating SD to √(Σy^2/n - μ^2), solving for Σy^2 and subbing everything into Syy (which took about half a page, compared to the one line σ^2 x 8). I scribbled it down under the heading "Alternate method for part (b)", but I don't actually understand why it works. Is there some formula it's based on?
Yes if you look at a formula sheet and look at Syy, it will say that Syy = Σ(y-(mean of y))^2 , thats what it is based off. Because y - mean of y = Standard deviation
6. Very confused about showing Syy, I somehow showed it was 7.16 instead of 716, does anyone remember the numbers? I got sum of y^2 to be about 26900, and then did the Syy formula.
7. (Original post by jasmine9876)
I think it was 4 marks 2 marks for each. 2 marks for explaining whats gonna happen to the mean and sd and two for explaining why

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I'm pretty certain it was one each, I remember thinking that it was asking for a lot for one mark.
8. (Original post by SolomonP)
2 marks - for the question on mean/SD changes
3 marks - discussing the use of a Z distribution for the weights.

Both were different parts of the same Q.

EDIT: May very well have been 4 for the mean/SD thinking back, credit to jasmine9876
I'm pretty certain you're right
9. (Original post by leestitt)
Yes if you look at a formula sheet and look at Syy, it will say that Syy = Σ(y-(mean of y))^2 , thats what it is based off. Because y - mean of y = Standard deviation
Ahhh I was trying to look through the formula book to see if any of the formulae our teachers had told us not to look at were useful, but somehow it didn't click that y-[y bar] is standard deviation. I wonder if they wanted you to write out that definition to show that you knew what you were talking about (which I didn't, despite the fact that I stumbled across the answer). Anyway, the long-winded way should get the mark as well.
10. Anyone know the marks for the other questions?

Bee wiggle question
Response variable (1 mark)
Work out regression line (4 marks)
Use regression line to estimate when D=350, state if reliable (2 marks)

Sarah rebecca prob distribution
Make an equation with p and q (1 mark)
Find p (2 mark)
Hence find q (1 mark maybe 2??)
Find var x (2 mark, maybe 3 cos u had to find E(x squared) aswell)
Find E(R) (3 marks)
Probabilities of them winning a game (4 marks) split into two parts

Rainfall question
Find Syy (1 mark lol)
Work out R (2 marks)
State effect on pmcc with reason (2 marks)

Baby question
Work out width/height of bar (3 marks)
Linear intepolation for median (3 marks)
Show estimate of mean is... (2 marks)
Standard deviation (2 marks)
P(x<3) (2 marks i think)
Was shyan right to use normal distribution (3 marks)

Hotel question
Question about probability of booking a breakfast without room was (1 mark)
Working out the value of t was (4 marks) and then
Working out the value of U was (2 marks.)
The conditional probabilities of the people eating dinner question (2 marks for each part so 4 marks overall)
The part about estimating the amount of people from the coach who had dinner was (2 marks)

1st part (3 marks)
Finding how fast he can run to be in top 20% (3 marks)
Finding probability of X<u-30|x<u (3 marks)

Only have 62/75 marks here written down, anyone else remember the other 13? They are missing from the bee question and the rainfall question, I think i got the other ones completed
11. (Original post by ShatnersBassoon)
Ahhh I was trying to look through the formula book to see if any of the formulae our teachers had told us not to look at were useful, but somehow it didn't click that y-[y bar] is standard deviation. I wonder if they wanted you to write out that definition to show that you knew what you were talking about (which I didn't, despite the fact that I stumbled across the answer). Anyway, the long-winded way should get the mark as well.
12. (Original post by Florent venhari)
Might be in luck for an A! But defo a B

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I think that could be an A because the chances are C1 will skew their grade boundaries so your mark seems quite high. So S1 could possibly balance out.
13. (Original post by uk_shahj)
Anyone know the marks for the other questions?

Bee wiggle question
Response variable (1 mark)
Work out regression line (3 marks, may have been 4)

Sarah rebecca prob distribution
Make an equation with p and q (1 mark)
Find p (2 mark)
Hence find q (1 mark maybe 2??)
Find var x (2 mark, maybe 3 cos u had to find E(x squared) aswell)
Find E(R) (3 marks)
Probabilities of them winning a game (4 marks) split into two parts

Rainfall question
Find Syy (1 mark lol)
Work out R (2 marks)
State effect on pmcc with reason (2 marks)

Baby question
Work out width/height of bar (3 marks)
Linear intepolation for median (3 marks)
Show estimate of mean is... (2 marks)
Standard deviation (2 marks)
P(x<3) (2 marks i think)
Was shyan right to use normal distribution (3 marks)

Hotel question
Question about probability of booking a breakfast without room was (1 mark)
Working out the value of t was (4 marks) and then
Working out the value of U was (2 marks.)
The conditional probabilities of the people eating dinner question (2 marks for each part so 4 marks overall)
The part about estimating the amount of people from the coach who had dinner was (2 marks)

1st part (3 marks)
Finding how fast he can run to be in top 20% (3 marks)
Finding probability of X<u-30|x<u (3 marks)

Only have 59/75 marks here written down, anyone else remember the other 16? They are missing from the bee question and the rainfall question, I think i got the other ones completed
On question 1, you got two marks, one for making an estimate when d = 250, then another for stating if it was reliable.
14. (Original post by iMacJack)
I think I put the PMCC deceased because the point was further away from the line of best fit?

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Jack Rember the PMCC WAS like -.72 or something and if itgot further way from the line the PMCC would increase as there would be less correlationtherefore getting closer to zero
15. Rep this is if you got 16 or 17 people had dinner. I wanna know if I'm not the only one
16. (Original post by NoahMal)
Jack Rember the PMCC WAS like -.72 or something and if itgot further way from the line the PMCC would increase as there would be less correlationtherefore getting closer to zero
Yh I overthought it, still looking at 71/72
17. (Original post by NoahMal)
Rep this is if you got 16 or 17 people had dinner. I wanna know if I'm not the only one
You arent the only one, but you're wrong, i posted a model solution to how to do it

How to get 33 customers model answer!

P(D|RnB) = 0.45 and P(D|RnB' = 15/37

It says that 40 customers have rented a room and eaten breakfast
It also says that 37 have rented a room and not had breakfast

Well, we worked out the chance of them having dinner given those conditions in the two previous parts, so all we needed to do was 40*0.45 + 37 * 15/37 to come to our answer of 18+15 = 33 customers.

Hope this clears it up
18. Do we have an unofficial markscheme yet?
19. Does anyone have the paper? If so can you post qu 2? Thanks
20. Unofficial mark scheme?

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