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

    3
    ReputationRep:
    Suppose that H is the number of heads obtained in two tosses of a fair coin. Thenvar(H)??

    And also this question:

    Of the A-level students at a certain school, 60% of those taking Mathematics also takeEconomics, while 30% of those not taking Mathematics take Economics. Overall, 35%of the A-level students at this school take Mathematics. A student is selected randomlyfrom those taking Economics. The probability that this student is also studyingMathematics is:
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by Teddysmith123)
    Suppose that H is the number of heads obtained in two tosses of a fair coin. Thenvar(H)??

    And also this question:

    Of the A-level students at a certain school, 60% of those taking Mathematics also takeEconomics, while 30% of those not taking Mathematics take Economics. Overall, 35%of the A-level students at this school take Mathematics. A student is selected randomlyfrom those taking Economics. The probability that this student is also studyingMathematics is:
    What have you tried for both of those questions?
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by SeanFM)
    What have you tried for both of those questions?
    For the first one I honestly have no clue, and for the second one I tried having a numerical value of 100 as total people in the year to make the question simpler but I just don't know how to get to the answer of 0.52?
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by Teddysmith123)
    For the first one I honestly have no clue, and for the second one I tried having a numerical value of 100 as total people in the year to make the question simpler but I just don't know how to get to the answer of 0.52?
    Can you think of any kind of model that would help for question 1?

    For part two, how about a certain kind of diagram? Putting in a number like 100 might work but you've probably been caught out by the probabilities. With the certain kind of diagram, you need to 'start in the middle and work outwards'.
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by SeanFM)
    Can you think of any kind of model that would help for question 1?

    For part two, how about a certain kind of diagram? Putting in a number like 100 might work but you've probably been caught out by the probabilities. With the certain kind of diagram, you need to 'start in the middle and work outwards'.
    I thought PDF would work for one but have no idea how to construct it and I know 2 requires a venn diagram but again I don't know how to construct it right?
    Offline

    2
    ReputationRep:
    For the first one draw a table with x, P(X=x), xP(X=x) and x^2 P(X=X) and use the formula for the variance Var(X)=sum(x^2 P(X=x)) - (sum(xP(X=x)))^2
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by Teddysmith123)
    I thought PDF would work for one but have no idea how to construct it and I know 2 requires a venn diagram but again I don't know how to construct it right?
    Doing something with the PDF is one way of doing it. What exam board are you with?

    Correct. You have to 'start in the middle and work outwards' - what could this mean, when you just have two circles in your Venn diagram with one overlapping section?
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by SeanFM)
    Doing something with the PDF is one way of doing it. What exam board are you with?

    Correct. You have to 'start in the middle and work outwards' - what could this mean, when you just have two circles in your Venn diagram with one overlapping section?
    edexcel

    and i really don't understand could you please show me with a diagram? P
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by Teddysmith123)
    edexcel

    and i really don't understand could you please show me with a diagram? P
    One way of doing the first question has been given above.

    Another way (I'm not sure if it is acceptable or not) is to recognise that it can be modelled by a binomial distribution with n = ?? and p = ??, and then use the result that the variance of such a distribution is ??



    Imagine one circle says Mathematics and the other says Economics. When I say that you have to 'start in the middle and work outwards', it means that you have to start in the overlap (it would be the same idea if there were 3 difference subjects). Because you know that P(someone studies Mathematics) = P(Someone studies Mathematics and Economics) + P(Someone studies Mathematics but not Economics).
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by SeanFM)
    One way of doing the first question has been given above.

    Another way (I'm not sure if it is acceptable or not) is to recognise that it can be modelled by a binomial distribution with n = ?? and p = ??, and then use the result that the variance of such a distribution is ??

    [img]http://www.thereligionteacher.com/wp-content/uploads/2011/10/blank-venn-diagram-300x165.png[/img]

    Imagine one circle says Mathematics and the other says Economics. When I say that you have to 'start in the middle and work outwards', it means that you have to start in the overlap (it would be the same idea if there were 3 difference subjects). Because you know that P(someone studies Mathematics) = P(Someone studies Mathematics and Economics) + P(Someone studies Mathematics but not Economics).
    OK so i understand how to find var(h) but still don't get how to solve the venn diagram
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by Teddysmith123)
    OK so i understand how to find var(h) but still don't get how to solve the venn diagram
    Sorry, the image didn't work because one of the tags were in bold.



    Imagine one says Economics and the other says Economics. You have to start in the middle - so what proportion of students study both Maths and Economics?
    Offline

    8
    ReputationRep:
    (Original post by Teddysmith123)
    Suppose that H is the number of heads obtained in two tosses of a fair coin. Thenvar(H)??

    And also this question:

    Of the A-level students at a certain school, 60% of those taking Mathematics also takeEconomics, while 30% of those not taking Mathematics take Economics. Overall, 35%of the A-level students at this school take Mathematics. A student is selected randomlyfrom those taking Economics. The probability that this student is also studyingMathematics is:
    Go to exam solutions.org he will help you out really well.

    I used to get D's and E's in core maths and statistics but since I started watching his tutorials I got nothing short of full marks in all my s1 papers.

    He is especially good at edexcel and has video tutorials for each topic and also for every edexcel maths a level paper from 2007-2014

    so why not check him out?
 
 
 
  • 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
    Would you like to hibernate through the winter months?
    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

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