Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    15
    ReputationRep:
    Hi - I just completed the June 14 S2 paper - I have a few small issues I wanted to get clarified, even if you're able to help out with just one I'd be much appreciative.

    Link to the paper: https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

    1 (b) - I got 1 mark for stating lambda = 3/2, I don't quite understand how the probability of the next patient arriving before 11:45 is = to 1-p(0), though? (Silly error/misunderstanding, I'm sure. Nonetheless I'd like to resolve it)

    2 (d) - Surely this would be P(t>=7) / P(t>3), not p(t>7)/p(t>3)? Because it says 'at least 7 minutes' implying >=?

    3 (d) - a good question to try for anyone with spare time! No help required for this one!

    4 (c) - Again not really in need of help, but is there any clues that you'll need to flip the binomial from b(100,0.975) to b(100,0.025)?

    6 (c) - Why is it that we set the 2/9 x - 1/9 bit = 0.5? Is it because the median is in between 1<x<4 (3rd value??)

    Cheers, silly questions I am aware, but any help just to make sure I really get this module secure would be grately appreciated.

    Zacken Ayman! etc, all the maths geniuses!
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by iMacJack)
    Hi - I just completed the June 14 S2 paper - I have a few small issues I wanted to get clarified, even if you're able to help out with just one I'd be much appreciative.

    Link to the paper: https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

    1 (b) - I got 1 mark for stating lambda = 3/2, I don't quite understand how the probability of the next patient arriving before 11:45 is = to 1-p(0), though? (Silly error/misunderstanding, I'm sure. Nonetheless I'd like to resolve it)

    2 (d) - Surely this would be P(t>=7) / P(t>3), not p(t>7)/p(t>3)? Because it says 'at least 7 minutes' implying >=?

    3 (d) - a good question to try for anyone with spare time! No help required for this one!

    4 (c) - Again not really in need of help, but is there any clues that you'll need to flip the binomial from b(100,0.975) to b(100,0.025)?

    6 (c) - Why is it that we set the 2/9 x - 1/9 bit = 0.5? Is it because the median is in between 1<x<4 (3rd value??)

    Cheers, silly questions I am aware, but any help just to make sure I really get this module secure would be grately appreciated.

    Zacken Ayman! etc, all the maths geniuses!
    I sat this very paper. :moon: but it is too late in the day. If n one has got back to you later, you are welcome to quote me
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by SeanFM)
    I sat this very paper. :moon: but it is too late in the day. If n one has got back to you later, you are welcome to quote me
    Bit of a hard paper!
    Offline

    3
    ReputationRep:
    (Original post by iMacJack)
    1 (b) - I got 1 mark for stating lambda = 3/2, I don't quite understand how the probability of the next patient arriving before 11:45 is = to 1-p(0), though? (Silly error/misunderstanding, I'm sure. Nonetheless I'd like to resolve it)
    They're calculating P(X >= 1). I'm not sure exactly why though, I'm struggling to understand the wording as well. Perhaps Zacken or Sean can clarify.

    2 (d) - Surely this would be P(t>=7) / P(t>3), not p(t>7)/p(t>3)? Because it says 'at least 7 minutes' implying >=?
    Continuous probability - whether your inequality is strict or not doesn't make a difference. You're correct in saying that it should be equal to from interpreting the language (and definitely would be correct for a discrete distribution), but in the calculation side of things it hardly makes a difference because a continuous random variable can't actually be equal to any one number; P(T = 7) = 0.

    4 (c) - Again not really in need of help, but is there any clues that you'll need to flip the binomial from b(100,0.975) to b(100,0.025)?
    Well, if you want to approximate using a Poisson distribution your lambda would be much too large if you approximated from B(100, 0.975).

    6 (c) - Why is it that we set the 2/9 x - 1/9 bit = 0.5? Is it because the median is in between 1<x<4 (3rd value??)
    There's no better way to do this than trial and error.

    If you plug in the last value of the range into your first function, (x = 1 into x^2/9) you'll observe that F(1) = 1/9, which is much less than 0.5. If you plug in x = 4 into the second function, you'll get F(4) = 0.777..., which means that the median must lie here.
    Online

    22
    ReputationRep:
    For Q1:

    Switch the parameter to reflect the new time interval, hence 1.5.

    Now, the probability that the next patient arrives in that time interval is the probability of X = 1 (that's one patient arrivingin the interval) or X = 2, or X = 3, etc...

    So you want P(X >= 1) = 1 - P(X=0)
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by Ayman!)
    They're calculating P(X >= 1). I'm not sure exactly why though, I'm struggling to understand the wording as well. Perhaps Zacken or Sean can clarify.



    Continuous probability - whether your inequality is strict or not doesn't make a difference. You're correct in saying that it should be equal to from interpreting the language (and definitely would be correct for a discrete distribution), but in the calculation side of things it hardly makes a difference because a continuous random variable can't actually be equal to any one number; P(T = 7) = 0.



    Well, if you want to approximate using a Poisson distribution your lambda would be much too large if you approximated from B(100, 0.975).



    There's no better way to do this than trial and error.

    If you plug in the last value of the range into your first function, (x = 1 into x^2/9) you'll observe that F(1) = 1/9, which is much less than 0.5. If you plug in x = 4 into the second function, you'll get F(4) = 0.777..., which means that the median must lie here.
    Ahhhhhhhhhh right I see! Thank you for the clarifications!


    (Original post by Zacken)
    For Q1:

    Switch the parameter to reflect the new time interval, hence 1.5.

    Now, the probability that the next patient arrives in that time interval is the probability of X = 1 (that's one patient arrivingin the interval) or X = 2, or X = 3, etc...

    So you want P(X >= 1) = 1 - P(X=0)
    So it's the probability of one OR more of the patients arriving, not only one? In which case, P(x>=1) makes sense.

    Thank you!

    Cheers guys!
    Offline

    3
    ReputationRep:
    (Original post by Zacken)
    For Q1:

    Switch the parameter to reflect the new time interval, hence 1.5.

    Now, the probability that the next patient arrives in that time interval is the probability of X = 1 (that's one patient arrivingin the interval) or X = 2, or X = 3, etc...

    So you want P(X >= 1) = 1 - P(X=0)
    So any number of patients could arrive in the first 15 mins, so long that the first arrives then? Makes sense now.


    (Original post by iMacJack)
    Ahhhhhhhhhh right I see! Thank you for the clarifications!
    No worries!
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by Ayman!)
    So any number of patients could arrive in the first 15 mins, so long that the first arrives then? Makes sense now.




    No worries!
    Yeah - I think the wording can be slightly misleading at times
    Online

    22
    ReputationRep:
    (Original post by iMacJack)
    Yeah - I think the wording can be slightly misleading at times
    No, it's not misleading. There's a clear mathematical distinction between "one" and "exactly one"
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by Zacken)
    No, it's not misleading. There's a clear mathematical distinction between "one" and "exactly one"
    Chill. I was talking about in general with S2.
    Offline

    3
    ReputationRep:
    (Original post by iMacJack)
    Chill. I was talking about in general with S2.
    I agree. My comprehension skills aren't very good.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Has a teacher ever helped you cheat?
    Useful resources

    Make your revision easier

    Maths

    Maths Forum posting guidelines

    Not sure where to post? Read the updated guidelines here

    Equations

    How to use LaTex

    Writing equations the easy way

    Student revising

    Study habits of A* students

    Top tips from students who have already aced their exams

    Study Planner

    Create your own Study Planner

    Never miss a deadline again

    Polling station sign

    Thinking about a maths degree?

    Chat with other maths applicants

    Can you help? Study help unanswered threads

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Write a reply...
    Reply
    Hide
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.