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

    0
    ReputationRep:
    I have been struggling with this probability question for a while now. I really have no idea where to go. Any help you can give me would really be appreciated. I have answered (a) and (b) but the rest of it has me stumped.

    The answer to part a is 0.064 and b is 0.216.

    A man with eczema has a 0.4 chance of suffering symptoms on a given day. In a three-day period, what is the chance of him experiencing symptoms on:

    (a) 3 days
    (b) none of the days
    (c) exactly 2 days
    (d) at least one day
    (e) the final day
    P.S the answers are
    (a) 0.064
    (b) 0.216
    (c) 0.288
    (d) 0.784
    (e) 0.144
    Offline

    1
    ReputationRep:
    Are you familiar with binomial distribution? I was able to get an answer to C by using it. I haven't attempted the others yet.

    C:
    Spoiler:
    Show
    X~B(3,0.4)
    P(x=2)
    3C2 x (0.4)2 x (0.6)1 = 0.288


    D:
    Spoiler:
    Show
    X~B(3,0.4)
    P(x=0)
    3C0 x (0.4)0 x (0.6)3 = 0.216

    1 - 0.216 = 0.784


    E:
    Spoiler:
    Show
    0.62 x 0.4 = 0.144


    EDIT: There's my working out above. Try and have a go at learning binomial distribution and then tackling the questions above, before looking at how I did it.

    P.S

    If you're not very good at S1, believe me, you aren't the only one. I'm finding it difficult.
    Offline

    0
    ReputationRep:
    Part e follows a geometric distribution to be more precise
    Offline

    16
    ReputationRep:
    (Original post by Arg)
    ...
    As has been said this is binomial distribution

    If you are unsure of the formulae try to think through the questions

    Exactly 2 days could be

    YYN
    YNY
    NYY

    The P(YYN) = 0.4 x 0.4 x 0.6

    The other probabilities are the same



    For at least one day, you just need to consider NNN and take this away from 1 ... can you see why?



    I am afraid that I disagree with the answer for (e) if that is the actual question
    • Study Helper
    Online

    13
    Study Helper
    Agree with TenOfThem.

    The answer to (e) is incorrect if that's the question exactly as worded.

    If (e) was "the final day only", then the given answer would be correct.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by TenOfThem)
    The P(YYN) = 0.4 x 0.4 x 0.6

    The other probabilities are the same
    I have never heard of binomial distribution before.
    Also 0.4 x 0.4 x 0.6 = 0.096
    Which is not the answer.

    (Original post by TenOfThem)
    For at least one day, you just need to consider NNN and take this away from 1 ... can you see why?
    No.

    (Original post by TenOfThem)
    I am afraid that I disagree with the answer for (e) if that is the actual question
    (Original post by ghostwalker)
    Agree with TenOfThem.

    The answer to (e) is incorrect if that's the question exactly as worded.

    If (e) was "the final day only", then the given answer would be correct.

    That is the actual question and actual answer. I suppose it is possible that my sheet is wrong.
    Offline

    16
    ReputationRep:
    (Original post by Arg)
    I have never heard of binomial distribution before.
    Not sure why you are doing these question then

    Also 0.4 x 0.4 x 0.6 = 0.096
    Which is not the answer.
    Because you have not included the other options

    I only showed Yes Yes No ... there are other possibilities ... for example Yes No Yes

    No.
    hmmmmm

    You cannot see that you either have No No No or at least one day has to be Yes?

    That is the actual question and actual answer. I suppose it is possible that my sheet is wrong.
    Your sheet is wrong
 
 
 
  • 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.