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# Probabilities & Statistics 1 - OCR (not MEI) - jan 25th 2012 discussion

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1. (Original post by mcquitmp)
Well it may seem that way but I'm just a concerned parent.

If you don't trust me then fine - all you need to answer is the first bit - what marks were the last couple of questions worth so I can work out the potential impact on her score.

I've no need to cheat to get a score on these exams as I'm fairly confident with a few days prep I'd get 100% in them all if I needed to take them but with a First Class honours degree in microelectronic systems design - I'll give that a pass and not waste my time.

If you are stuck on a questions just ask me.
Question 8 was 8 marks I think.

Question 9 was 12 marks.

So altogether 20 marks.
2. (Original post by Jedicake)
P(X=x) =
thanks
3. Predictions for the A grade and 100 UMS marks? It seems people found it quite hard so A might go below the 57 mark.
4. (Original post by jammy274)
Sorry, I'll try to explain better.
Last part of question 8 you have to find probability that there are more red than blue (or the other way around I can't remember). For the part before that you had to work out the probability that there are 11 of each. so you do P(R=11) 22C11 x 0.5^11 x 0.5^11. Which comes to about 0.168.
The only possibilities are that Red and Blue have the same number, there are more red, or there are more blue. Because p = 0.5 the probability that there are more red or more blue are the same. So you do 1 - 0.168, then divide by two because the other two outcomes are equally likely.

And for the last part of question 9, the only possible combinations of making 28 and 9,8,7,4 and 9,8,6,5. so to work out out the probability that it's 9,8,7,4 you do 1/9 x 1/8 x 1/7 x 1/6 = 1/3024 then x by 4! because they can be in any order. Then you do the same for 9,8,6,5 so you x by 2. That should give you 48/3024 or 0.0159
thanks
5. For question 7 (that 60% of voters being women one)...was that a geometric distribution?
6. (Original post by sa.chan)
I also got 2/3cm too.

For the question where you had the 9 numbered discs, what did people get?
I got 4! for the first part because it said in the question Andrea picks 4 discs and puts them down in a random order. So I thought it was how many arrangements can you be made from the 4 that Andrea picked and not how many different combinations of 4 she could pick...

However, everyone else I've talked to did something like 9C4 instead so I'm thinking I'm probably wrong and got confused reading the question..
I got this too
7. (Original post by Ree69)
For question 7 (that 60% of voters being women one)...was that a geometric distribution?
Yes it was
8. (Original post by Ree69)
For question 7 (that 60% of voters being women one)...was that a geometric distribution?
yeh it was (X~Geo(0.6))
9. (Original post by jammy274)
Yes it was
Oh phew
10. (Original post by mcquitmp)
Well it may seem that way but I'm just a concerned parent.

If you don't trust me then fine - all you need to answer is the first bit - what marks were the last couple of questions worth so I can work out the potential impact on her score.

I've no need to cheat to get a score on these exams as I'm fairly confident with a few days prep I'd get 100% in them all if I needed to take them but with a First Class honours degree in microelectronic systems design - I'll give that a pass and not waste my time.

If you are stuck on a questions just ask me.
more like an overconcerned obssessive parent? shouldnt your daughter be asking the questions if she cares?
also theres no need to boast about these exams

YOU DIDNT TAKE THE EXAM YOUR DAUGHTER DID SO LEAVE

also what did it mean by one unit is 2cm? was one unit one of those tiny squares, or 1 unit made up from a 10x10 of the little squares
11. (Original post by dellprinter)
more like an overconcerned obssessive parent? shouldnt your daughter be asking the questions if she cares?
also theres no need to boast about these exams

YOU DIDNT TAKE THE EXAM YOUR DAUGHTER DID SO LEAVE

also what did it mean by one unit is 2cm? was one unit one of those tiny squares, or 1 unit made up from a 10x10 of the little squares
I've run out upvotes but if i could i would, what a tool.
12. (Original post by dellprinter)
also what did it mean by one unit is 2cm? was one unit one of those tiny squares, or 1 unit made up from a 10x10 of the little squares
It meant 10x10 little squares cos it was referring to the F.D units, they're worded stupidly
13. (Original post by spiders-design)
Anyone else notice the mistake. For the question where you had to say which graph was the geometric distribution there was a value for 0 which is not possible. Although it wouldn't have prevented anyone from getting that question right they may have then got the next one wrong as they may have thought that it returns the number of failures rather than the number of trials upto and including the success.

I think I got 100 UMS just not sure whether it was 100% or not. Might have made a silly mistake somewhere.
I noticed this too. I guessed that they thought V was correct, but then used some spare paper to explain why I thought it was wrong.
Hopefully, that will cover my tracks if it turns out to be a repeat of last year's exams cock-ups.
14. (Original post by jammy274)
It meant 10x10 little squares cos it was referring to the F.D units, they're worded stupidly
15. (Original post by dellprinter)
2/3 i believe?
16. would i get the question for regression line completely wrong if i worked it out for x on y instead of y on x. got x=66.8-0.7y
17. Hey everyone,

For the height being 2/3, I put that that the class would be between 9.5 and 15 so the width would 5.5 and my final answer was 4/11 :/
I thought 15 was the last class so you can't have 15.5

For 9, I put 3024 for part 1, 1680 for part 2 and I got 1/63 for the last one as well I messed up on part 3 because I put 5/9 * 4/8 * 3/7 *3/6 rather than 4/6 (
18. For regression line I got something like y=-0.75 + 75
19. (Original post by dellprinter)
2/3 cm
20. (Original post by jammy274)
Sorry, I'll try to explain better.
Last part of question 8 you have to find probability that there are more red than blue (or the other way around I can't remember). For the part before that you had to work out the probability that there are 11 of each. so you do P(R=11) 22C11 x 0.5^11 x 0.5^11. Which comes to about 0.168.
The only possibilities are that Red and Blue have the same number, there are more red, or there are more blue. Because p = 0.5 the probability that there are more red or more blue are the same. So you do 1 - 0.168, then divide by two because the other two outcomes are equally likely.

And for the last part of question 9, the only possible combinations of making 28 and 9,8,7,4 and 9,8,6,5. so to work out out the probability that it's 9,8,7,4 you do 1/9 x 1/8 x 1/7 x 1/6 = 1/3024 then x by 4! because they can be in any order. Then you do the same for 9,8,6,5 so you x by 2. That should give you 48/3024 or 0.0159
That's what I got for both What did everyone get for the mean and standard deviation?
My sd was around 3.07 I think

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