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# OCR MEI - S1 - 20th May 2015 watch

1. Can someone amazing pls post an unofficial mark scheme for this paper? 😘👌
2. (Original post by Spelly456)
Would I lose a mark for putting 1.00 (3sf) rather than 1 for the second conditional probability question?
Nope, although in the context of the question, the answer is fairly obviously 1, and calculation wasn't required, but you should not lose a mark for that.
3. for the hyp testing I did the critical region method (I totally didn't realise you could have used the other method, and I hadn't revised that method anyway)
so I got X is more than equal to 20 as the region
so I rejected the alternate hyp
so the drug wasn't more effective

but for the second question I got the critical region as x greater than or equal to 19, so I accept alternate hyp and the drug was more effective?

did anyone get this?
4. what did you get for the first standard deviation question?
5. (Original post by Kira Yagami)
Did people get 0.0523 for the question about the probability that all 3 will be the same sweet
yup!
6. (Original post by Bobhopkins05)
for the hyp testing I did the critical region method (I totally didn't realise you could have used the other method, and I hadn't revised that method anyway)
so I got X is more than equal to 20 as the region
so I rejected the alternate hyp
so the drug wasn't more effective

but for the second question I got the critical region as x greater than or equal to 19, so I accept alternate hyp and the drug was more effective?

did anyone get this?
Yep that's the general consensus for the correct answer - first part accept H0, second part reject H0.
7. Alright, finally managed to get these to upload.

So this is the full question paper, one page per image, with my answers scrawled on. The decimals are rounded to 3sf or 4sf wherever appropriate, so if your answer doesn't match that then check if it does when rounded to 3 or 4 significant figures. The only one I'm unsure of is the last one, since there seem to be many different answers that people are getting, but it seems like the most logical answer to me.

Daniel McLovin said he would post an unofficial markscheme if somebody had the question paper, so you can also wait for that if my messy final answers aren't sufficient
8. (Original post by ZoeWoah)
How much was the last question out of?
The box plot was 5, the first probabilities were 6 total, the next part was 2, the next part was 3 iirc
9. (Original post by JamesExtra)
Is it ok to say "there is an outlier at the upper end" rather than there are some outliers at the upper end?
Yeah think its fine
10. (Original post by Daniel McLovin)
Did anyone happen to get a Question booklet out? I'll make a mark scheme if there is.
Posted my question paper now, just above this post
11. (Original post by Kira Yagami)
Did people get 320/12 for the mean of the stem and leaf, 31 for the mode and can't remember the median but it was the 6.5th value
Yep exactly what I got
12. (Original post by Duskstar)
It depends on the mark scheme slightly, but I think examiners are allowed to make a judgement call, and if they notice what happened you'll either lose the A mark on each question, or possibly they'll take an arbitrary 1-3 marks away from that question but mark everything as though the 3 wasn't there. I'm not an examiner so don't take my word for it :P
both of them scenarios you put there are me gaining some marks, do you think there is any way I could have lost all 18 marks if I did the right method all the way through but used 17 instead of 20?
13. (Original post by thecalmmorning)
I had no idea how to do that
It was the binomial probability of (1 6, 2 not 6), (2 6, 1 not 6), (3 6) added together.
14. (Original post by bethygirl)
both of them scenarios you put there are me gaining some marks, do you think there is any way I could have lost all 18 marks if I did the right method all the way through but used 17 instead of 20?
No, definitely not. I think the most likely scenario (assuming you put down all your workings and did the correct method) is that you would get all method marks and drop all the accuracy marks (normally 1 mark per question, but I think 1 part doubled up, so 6 marks total from that).
15. Anyone walk me through 8ii B) and 8 v) ? For 8ii B I thought I got 1.

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16. (Original post by iamJOM)
Posted my question paper now, just above this post
Thank you, and did you do critical regions for the hypothesis tests?
17. (Original post by Duskstar)
Thank you, and did you do critical regions for the hypothesis tests?
Yup, {20} for the 1% significance and {19, 20} for the 5%.
18. (Original post by Kichelle)
Anyone walk me through 8ii B) and 8 v) ? For 8ii B I thought I got 1.

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For 8ii B) it's (what Duskstar says below this post, I answered the wrong question the first time)

For 8v there are a few different answers floating around, but the way that I did it is as if Ben picks two that he doesn't like (i.e. two cherries) resulting in him having to pick more than two to get one that he wants. This gives (6/20)*(7/19) which results in 3/38
19. (Original post by Kichelle)
Anyone walk me through 8ii B) and 8 v) ? For 8ii B I thought I got 1.

Posted from TSR Mobile
8ii) B) was probability of all picking orange OR all cherry etc..

That made it (7*6*5 + 6*5*4 + 4*3*2 + 3*2*1) / (20 * 19 * 18)

8v) there is a lot of dispute about. I'll repost what I posted earlier:

What I did was 1 - (14/20) - (6/20) * (14/19) - (6/20) * (5/19) * (14/18)

I'm not 100% sure in what I did - I hope it's correct, but it's possible the third probability wasn't needed, and I haven't had time to think it through properly since the exam lol.
20. Any guesses to what mark out of 72 full UMS will be? or what mark needed for an A?

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