Results 1 to 5 of 5

Math Help - probaility #2

  1. #1
    Member
    Joined
    Mar 2010
    Posts
    122

    probaility #2

    A certain part of a machine can be in one of two states: working (W) or undergoing
    repair (R). A working part fails during the course of a day with probability a; assume
    that failure occurs at the end of the day so that the part can be labelled as in working
    condition for that day. Having failed, it undergoes repair on the following working day.
    The probability that a part undergoing repair is in working order by the start of the
    following working day is b.
    Assume that the part is in working condition on Monday morning. What is the probability
    that it is working on Wednesday (2 days later)?

    I have gotten (1-a)^2+(1-a)ab but i am not sure if i have done it wrong. I have basically used a tree diagram and used the appropriate branches.Can anyone check my solution because there is no answer for the odd questions in the book
    Last edited by mr fantastic; August 6th 2010 at 08:10 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by ulysses123 View Post
    A certain part of a machine can be in one of two states: working (W) or undergoing
    repair (R). A working part fails during the course of a day with probability a; assume
    that failure occurs at the end of the day so that the part can be labelled as in working
    condition for that day. Having failed, it undergoes repair on the following working day.
    The probability that a part undergoing repair is in working order by the start of the
    following working day is b.
    Assume that the part is in working condition on Monday morning. What is the probability
    that it is working on Wednesday (2 days later)?

    I have gotten (1-a)^2+(1-a)ab but i am not sure if i have done it wrong. I have basically used a tree diagram and used the appropriate branches.Can anyone check my solution because there is no answer for the odd questions in the book
    There are two ways for it to be working on Wednesday. They are, using the states of the part,

    WWW (means: W on Mon, W on Tue, W on Wed)
    WRW

    So it's (1-a)^2 + ab. Where did your extra (1-a) come from?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Mar 2010
    Posts
    122
    W'=it has wrecked at the end of the day:

    Therefore i get:

    WWW+WW'R

    1) it is working at the end of monday and it is working at the end of tuesday and therefore ready at the start of
    wednesday(1-a)^2

    2)it is working at the end of monday, but fails at the end of tuesday but is repaired on wednesday in time for use on wednesday
    (1-a)ab
    I am not 100% certain can someone else try this?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by ulysses123 View Post
    2)it is working at the end of monday, but fails at the end of tuesday but is repaired on wednesday in time for use on wednesday
    The question is worded carefully to avoid things like this. Whatever the state of the part in the morning is what we say the state of the part is for the entire day. A part is marked for repair at the end of the day, meaning there's no way for a part to break in one day and still be ready the next day.

    It should be 2) it fails on monday (but we consider it working on monday because it started out working), but is repaired on tuesday, giving ab.
    Last edited by undefined; August 6th 2010 at 07:06 AM. Reason: clarity
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Mar 2010
    Posts
    122
    i have read this a few times since last night.Sometimes i think you a right and sometimes i think i am right!
    I''l ask my teacher on monday and then post what she tells me.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Probaility And Combination Question
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: October 27th 2010, 08:19 AM
  2. probaility Question
    Posted in the Statistics Forum
    Replies: 2
    Last Post: August 6th 2010, 04:37 AM
  3. test statistic and probaility
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: May 6th 2010, 06:10 PM
  4. probaility type 1 error
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: May 3rd 2010, 04:50 PM
  5. probaility analysis
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: November 22nd 2008, 12:13 PM

Search Tags


/mathhelpforum @mathhelpforum