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# OCR MEI - S1 - 20th May 2015 watch

1. http://www.mei.org.uk/files/papers/2011_Jan_s1.pdf

Can someone help me with 7v on this, i dont know how the variation changes with the addition of the equation?
2. (Original post by liverpool2044)
http://www.mei.org.uk/files/papers/2011_Jan_s1.pdf

Can someone help me with 7v on this, i dont know how the variation changes with the addition of the equation?
yeah by timing something it changes the variation (makes the s.d. more varied) only adding makes no difference
3. M

(Original post by Azula)
yeah by timing something it changes the variation (makes the s.d. more varied) only adding makes no difference
I dont understand the mark scheme it says you need to square the sd and the 1.15? why?
4. (Original post by liverpool2044)
M

I dont understand the mark scheme it says you need to square the sd and the 1.15? why?
times the standard deviation by 1.15,
then square this to get the correct variance
try to memorise that
5. (Original post by Azula)
times the standard deviation by 1.15,
then square this to get the correct variance
try to memorise that
does it have any reference to ex^2-ex? = var(x)
6. (Original post by liverpool2044)
does it have any reference to ex^2-ex? = var(x)
I'm sure it doesn't matter as either method is correct

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7. As someone above mentioned how do people approach sig figs with this? I usually do 4 for any binomial calculations and then 3 for the rest. But in marking a past paper just now there seems to be no consistency in how many the mark scheme uses.
8. (Original post by Bruhh)
As someone above mentioned how do people approach sig figs with this? I usually do 4 for any binomial calculations and then 3 for the rest. But in marking a past paper just now there seems to be no consistency in how many the mark scheme uses.

Candidates are expected to give numerical answers to an appropriate degree of accuracy. 3 significant figures may often be the norm forthis, but this always needs to be considered in the context of the problem in hand. For example, in quoting probabilities from Normal tables,we generally expect some evidence of interpolation and so quotation to 4 decimal places will often be appropriate. But even this does notalways apply – quotations of the standard critical points for significance tests such as 1.96, 1.645, 2.576 (maybe even 2.58 – but not 2.57)will commonly suffice, especially if the calculated value of a test statistic is nowhere near any of these values. Sensible discretion must beexercised in such cases.

this is whats mentioned by the spec. Id keep to four just to be safe
9. Can someone help me on this s1 question :http://vle.woodhouse.ac.uk/topicdocs...2007Jan.pdf7iv.
I dont understand how they got the answer. My calculation is as follows: 200*(4/9) will give me the expected that will germinate. And as the same amount are destroyed elsewhere, 200-(200*(4/9)). Which yields 111.1. Then 0.85*111.1 gives me the answer as 94.4. Which is wrong.
10. (Original post by zirak46)
I struggled with two tailed just two days ago but I hacked it haha
Okay so firstly, you need to know hypothesi testing for significance levels & critical region
One tail involes (lets say prob is 0.5)
Ho : p = 0.5
H1 : p > 0.5 OR p < 0.5 (depending on ques, as you probs know)
and then you either do sig level version:
In the ques you get x value (say its x = 14)
if p > 0.5 then P(X>/14)
if p < 0.5 then P(X</14) that means less than equal to btw haha
Now whichever it is, you compare to sig level (has to be below it)

or do critical region version:
if p > 0.5 then compare to high tail of critical region (trial & error)
if p < 0.5 then compare to low tail of critical region (both have to be below it)

For two tail testing, it involves:
Ho : p = 0.5
H1 : p DOESNT EQUAL 0.5
and then you do same thing but for sig level version:
-you HALF sig level
e.g. so say x = 12 and its two tail and sig level is 5% (0.05)
it'll be P(X</12) compared to 0.025

for CR version:
-you HALF sig level
-you do for both p > 0.5 AND p < 0.5
e.g. say sig level is 5% (0.05) and X~B(20, 0.5)
-check on tables for biggest n value for where P(X</ something) is less than 0.025
-check on tables for biggest n value for where P(X>/ something) is less than 0.025

Hope that made sense, if not, send a question & I'll happily do a question for you explaining all
Good luck

Just wanted to say that this is a great explanations! Thankyou!
11. (Original post by benwood)
My dad works in the printing department for OCR, he told me there's no point revising two tailed tests...
For real? Damn, did those over the weekend!
12. Hello,

Can anyone explain how to do Q5 ii, from the Jan 2013 exam?
13. (Original post by Purpledwarf)
Hello,

Can anyone explain how to do Q5 ii, from the Jan 2013 exam?
Do the chance of him not throwing a 6 10 times and take this from 1:
1-(5/6) to the power 10 gives 1-0.1615 so the answer is 0.8385.

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14. (Original post by megan*kate)
Do the chance of him not throwing a 6 10 times and take this from 1:
1-(5/6) to the power 10 gives 1-0.1615 so the answer is 0.8385.

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Thanks
16. (Original post by Slenderman)

Oh, apart from the combinations and permutations. Some of those are really difficult to get your head around
17. (Original post by iamJOM)

Oh, apart from the combinations and permutations. Some of those are really difficult to get your head around
Aha yeah those can be a pain. Just learn the equations, common question types and try to get as much practise.
18. hands up if youre gonna fail
19. (Original post by benwood)
My dad works in the printing department for OCR, he told me there's no point revising two tailed tests...
what else did your dad say, i would very much like to know
20. Im confused with critical region like sometimes they do both lower and upper tail and sometimes just the upper? Like how do ik when to do what?

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