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Edexcel S2 - 27th June 2016 AM Watch

  • View Poll Results: How did you find the Edexcel S2 exam?
    Very hard
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    152
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    (Original post by zombaldia)
    Yeah I guess that is lucky in a way



    Okay, thanks. I'll just try to do all the past papers over this weekend
    Good luck with that :P There's a ton of them
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    Sometimes the grade boundaries for S2 are so high. January 2011 72 for an A* and 69 for an A. I always make a few stupid mistakes but then again when doing past papers I don't check my answers even though I have ample time left (but that won't happen in the exam).
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    In the exam, do you actually have to write "Let X be the random variable...." and then write X~B(30,0.5), for example? Or can you just get away with writing the second part?
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    (Original post by apzoe)
    In the exam, do you actually have to write "Let X be the random variable...." and then write X~B(30,0.5), for example? Or can you just get away with writing the second part?
    You can get away with writing the second part only I think. On the mark scheme they put square brackets around "Let X be the random variable..." which implies that it is optional and not needed. If you have time to write it I would write it anyways for peace of mind.
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    (Original post by SeanFM)
    With the CDF, you can find the proportion of children whose estimate is ... blah blah blah.

    So that's the proportion (or probability, if you like) of children that are right.. and you have 80 people, so you would expect ... many to be right out of 80.
    Ok I feel stupid I should've got that
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    (Original post by target21859)
    Sometimes the grade boundaries for S2 are so high. January 2011 72 for an A* and 69 for an A. I always make a few stupid mistakes but then again when doing past papers I don't check my answers even though I have ample time left (but that won't happen in the exam).
    Best to get in the habit now, so you get a more realistic idea of your grade (I know it's not easy to do that with a mock exam or a past paper at home etc) but you could have / would have got some more marks.

    (Original post by AlphaArgonian)
    Ok I feel stupid I should've got that
    Don't beat yourself up about it. Mistakes are the best way to learn things, not getting things right.
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    Welp just starting S2 now as I had so many other exams to do, hopefully I can pick it up quickly
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    Another question: If in an exercise there are multiple parts (a, b, c etc), do you need to use different random variables (X, Y, M, etc) if they are defined differently?

    For example, in a the rate of change is 5 per minute, in b it is 10 per 2 minutes. Having different random variables does not change the solution, but may make it confusing?

    Hope you understood and thank you!
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    (Original post by Music With Rocks)
    Welp just starting S2 now as I had so many other exams to do, hopefully I can pick it up quickly
    Don't worry there aren't many topics and the same stuff comes up in the exams over and over again.
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    Are answers meant to give always to 3 or 4 sig fig?
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    (Original post by apzoe)
    Another question: If in an exercise there are multiple parts (a, b, c etc), do you need to use different random variables (X, Y, M, etc) if they are defined differently?

    For example, in a the rate of change is 5 per minute, in b it is 10 per 2 minutes. Having different random variables does not change the solution, but may make it confusing?

    Hope you understood and thank you!
    It'd be good practice.

    Because you'd be saying.. 'X is the number of .... in ... minutes/days/hours/whatever' so it wouldn't be sensible to still use X when you've changed the timeframe.
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    When testing to find the critical region, do we have to attempts, or can we just write down the correct boundary?
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    (Original post by LLk1)
    When testing to find the critical region, do we have to attempts, or can we just write down the correct boundary?
    A MS and how marks are awarded'll give an idea. From what I remember, you need to have the two numbers closest, show that you've compared them but.. that might not be necessary/misleading.
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    (Original post by SeanFM)
    Don't beat yourself up about it. Mistakes are the best way to learn things, not getting things right.
    I know but this felt like more common sense (mathematically speaking).
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    (Original post by AlphaArgonian)
    I know but this felt like more common sense (mathematically speaking).
    I dunno, I don't think it was particularly obvious. But you've seen it once now and that would be enough, and if you get asked something slightly different you can just kind of step back and think about how to solve it.
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    (Original post by SeanFM)
    Precisely.

    If we take a discrete distribution (no difference if it's continuous, but let's keep it simple), say X is a binomial distribution with p = p (some probability, doesn't matter, n= 20, say).

    And we pick a random number in that distribution, say 8. Then every number that the distribution can take (ranging from 0 to 20) is either going to be greater than 8, or less than or equal to 8. It sounds obvious/strange but we can use that. There is no value that X can take that isn't less than or equal to 8, or greater than 8, so  P(X \leq 8) + P(X > 8) = 1 as those two statements cover every number in X. You can generalise that for any x value from X,  P(X \leq x) + P(X > x) = 1 \Rightarrow  1 - P(X>x) = P(X \leq x) = CDF.
    Thank you so much, I understand it now.
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    Is there any model answers for like hypothesis testing because usually you do them in the same format but i get confused on like when it's one tailed/two tailed what number you use to work out probability and which way signs go
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    (Original post by Michaelj99)
    Is there any model answers for like hypothesis testing because usually you do them in the same format but i get confused on like when it's one tailed/two tailed what number you use to work out probability and which way signs go
    I can set out what I do/format I use and take a picture.
    I can do it in about an 45 mins to 1 hour if you don't mind? if you find two questions that will be helpful or I can do it with random letters and numbers?
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    i obtained a value of 2.367 when doing a normal approximation (correct contiunity correction) which value should i be using? 2.38 i think cos of rounding...

    in the exam i would list 2.36 and then 2.38 just as a guide (incase i should be picking 2.36 or use the mid value of the probabiltiy)
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    (Original post by tazza ma razza)
    i obtained a value of 2.367 when doing a normal approximation (correct contiunity correction) which value should i be using? 2.38 i think cos of rounding...

    in the exam i would list 2.36 and then 2.38 just as a guide (incase i should be picking 2.36 or use the mid value of the probabiltiy)
    2.37, I think you mean, and I would go for 2.37 (round to closest 2 d.p)
 
 
 
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