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# Ocr mei statistics 1 exam thread (24/05/13) watch

1. (Original post by jhitman)
Did anyone else get confused by what the last part of the last question wanted? correct me if I'm wrong, but I thought it said
"If *** hits the bulls eye in her first three throws she will not take her remaining 3 throws, but if not she will take all three throws"
I took that to mean she only doesn't take the last 3 throws if she hits bulls eyes in all of her first three throws?
I might be wrong, but that question seemed to be worded really ambiguously? Might they give me some marks since I got the maths right, just didn't understand what they wanted.

No it was if she hit bulls eye in at least 1 of her 3 throws she will not throw her next 3. So it was asking what was the chance of her hitting 3 bulls eyes

So it was:
Hitting 3 bulls eyes in the first 3 throws + hitting 3 bullseyes in the last 3 throws given that she hit no bullseyes in the first 3 throws.
2. (Original post by DarkWillow)
I did this also, and got 1=0.8684 & got 0.1316, so I rejected the null hypothesis as 0.1316 > 0.05
Is that wrong
Yeah I think it's wrong, as long as you put the paragraph about there being insufficient evidence you should still get 3-4 marks

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3. (Original post by princess_96)
for the hypothesis testing: as 13/20 guessed correctly

P(X≥13) = 1-P(X≤12) =0.13.. (something)

0.13>sig level

so accept null hypothesis

should be like that^ :/
I got all of that, but got confused & said reject null hypothesis :'/, I thought null hypothesis was h1
4. You know for the envelope question that said show P(x=15) = 0.05 I did 6x(1/6 x 1/5 x 1/4) which gave 0.05, but the way everyone else did it was (3/6 x 2/5 x 1/4) = 0.05 would i still get the marks because if you think about the question logically these are both correct
5. I did accept null hypothesis.

On the graph one, I read it off as 8/200 :/
EEK! is that okay? or was it 9?
6. (Original post by Mo_maths)
yh it was 0.0056.. something around that
i think i got 5.82x10^-3
7. damn that was a hard paper ....
8. Yeah I got 0.0056425 for last question but it didnt say you had to round to 3sf so just left it it was miss*miss*miss*hit*hit*hit + hit*hit*hit. Also I did 9/200*8/199 for the babies question idk if it was 8 it was a bit hard to read off but i ended up going for 9 but i dont think you should be penalised for getting 8 rather than 9 or anything like that. I did accept H0 aswell as there isnt enough evidence to suggest that people do better when guessing? Wasnt sure what the reason was for that but was definitely accept H0. The paper was pretty straight forward, hoping for an A. Rest of the paper was easy I think so pretty happy.
9. (Original post by superxo2)
I did accept null hypothesis.

On the graph one, I read it off as 8/200 :/
EEK! is that okay? or was it 9?
hopefully it doesn't matter to much because i read it off as 9. Then did 9/200 x 8/199
10. (Original post by Mo_maths)
yh it was 0.0056.. something around that
Omg! I got that too
ANYBoDY! Quote me if I'm wrong but is it right that if she hits a bullseye, the next probability is 0.2? If on the first hit she didn't, it was 0.9 and hitting a bullseye after that is 0.05 and on the third go, getting a bullseye is 0.2? Someone told me its 0.05 all the way through :/
I am actually ****ting myself cuz I put 0.2 n if its wrong, my whole question is wrong :/
11. what do people think grade boundaries will be?
12. (Original post by Mo_maths)
You know for the envelope question that said show P(x=15) = 0.05 I did 6x(1/6 x 1/5 x 1/4) which gave 0.05, but the way everyone else did it was (3/6 x 2/5 x 1/4) = 0.05 would i still get the marks because if you think about the question logically these are both correct
I did 1/ (nCr)

^ forgot what N and r was now...but I got 0.05
13. (Original post by x-Sophie-x)
0.0056245 I think and then round to 3sf.

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Yeah I got that. Took me a while to get my head around it :-)

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14. (Original post by Mo_maths)
You know for the envelope question that said show P(x=15) = 0.05 I did 6x(1/6 x 1/5 x 1/4) which gave 0.05, but the way everyone else did it was (3/6 x 2/5 x 1/4) = 0.05 would i still get the marks because if you think about the question logically these are both correct
Yep you would still get the marks!
15. anyone remember wat question 3 was
16. (Original post by juniorx)
hopefully it doesn't matter to much because i read it off as 9. Then did 9/200 x 8/199
hopefully we get method marks...
17. (Original post by Mo_maths)
You know for the envelope question that said show P(x=15) = 0.05 I did 6x(1/6 x 1/5 x 1/4) which gave 0.05, but the way everyone else did it was (3/6 x 2/5 x 1/4) = 0.05 would i still get the marks because if you think about the question logically these are both correct
Hmm not sure about that but i did go with 3/6 x 2/5 x 1/4
18. (Original post by Jojo_555)
Omg! I got that too
ANYBoDY! Quote me if I'm wrong but is it right that if she hits a bullseye, the next probability is 0.2? If on the first hit she didn't, it was 0.9 and hitting a bullseye after that is 0.05 and on the third go, getting a bullseye is 0.2? Someone told me its 0.05 all the way through :/
I am actually ****ting myself cuz I put 0.2 n if its wrong, my whole question is wrong :/
oh **** looks like i made a mistake then
19. (Original post by Jojo_555)
Omg! I got that too
ANYBoDY! Quote me if I'm wrong but is it right that if she hits a bullseye, the next probability is 0.2? If on the first hit she didn't, it was 0.9 and hitting a bullseye after that is 0.05 and on the third go, getting a bullseye is 0.2? Someone told me its 0.05 all the way through :/
I am actually ****ting myself cuz I put 0.2 n if its wrong, my whole question is wrong :/
You're right. Atleast I think so from what you are saying, is a bit confusing but the probability of hitting does change and isnt the same all the way through.
20. (Original post by Jojo_555)
Omg! I got that too
ANYBoDY! Quote me if I'm wrong but is it right that if she hits a bullseye, the next probability is 0.2? If on the first hit she didn't, it was 0.9 and hitting a bullseye after that is 0.05 and on the third go, getting a bullseye is 0.2? Someone told me its 0.05 all the way through :/
I am actually ****ting myself cuz I put 0.2 n if its wrong, my whole question is wrong :/
first hit was 0.9 for not hitting bullseye
after she's hit a bullseye, it's 0.2 for hitting a bullseye on the next go
if she didn't hit a bullseye, it's 0.05 for hitting a bullseye the next go
so i'm pretty sure you're right

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