Results 1 to 3 of 3

Math Help - Determining SD from percentage

  1. #1
    Member
    Joined
    Sep 2007
    Posts
    81

    Determining SD from percentage

    Hi all,

    This is a question from my mid-session test, I can understand most of the others I got wrong, but I have no idea how to answer this.

    Use the following to answer questions 14 & 15
    JETSTAR's daily flight from Sydney to Broken Hill is on time seventy per cent of the time. Over the next 10 days:

    Q15. The standard deviation of the relevant probability distribution (number of flights on time) is (closest to):

    a) 1.45,
    b) 2.10,
    c) 3.00,
    d) 7.00,
    e) Impossible to calculate from the information given.


    I'll avoid giving away my thinking to stop eliminating potential answers (because I got it wrong). Thanks folks.

    P.s. This is all the information for the question.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by Peleus View Post
    Hi all,

    This is a question from my mid-session test, I can understand most of the others I got wrong, but I have no idea how to answer this.

    Use the following to answer questions 14 & 15
    JETSTAR's daily flight from Sydney to Broken Hill is on time seventy per cent of the time. Over the next 10 days:

    Q15. The standard deviation of the relevant probability distribution (number of flights on time) is (closest to):

    a) 1.45,
    b) 2.10,
    c) 3.00,
    d) 7.00,
    e) Impossible to calculate from the information given.


    I'll avoid giving away my thinking to stop eliminating potential answers (because I got it wrong). Thanks folks.

    P.s. This is all the information for the question.
    Probability that a flight is on time is 0.7, assume that the timeliness of one flight is independent of that of any other. Then the number on time has a binomial distribution B(0.7,N) where N is the number of flights involved. You should know what the SD of this is.

    CB
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Sep 2007
    Posts
    81
    Cool thanks - got it.

    My problem was more reading the question. Just now it has clicked that it was a daily flight, I thought it was the total flights over 10 days, with the amount of flights being unknown.

    As a result, I said (e), because I didn't have enough information to answer the question.

    In fact N = 10 and I should be able to calculate it from there.

    Thanks again.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: August 26th 2011, 09:19 PM
  2. Replies: 1
    Last Post: May 9th 2010, 06:32 PM
  3. determining a and b
    Posted in the Calculus Forum
    Replies: 3
    Last Post: February 19th 2010, 01:45 PM
  4. Determining GDP
    Posted in the Business Math Forum
    Replies: 0
    Last Post: March 3rd 2009, 05:36 PM
  5. nid Help on determining A, B, C, and D T_T
    Posted in the Algebra Forum
    Replies: 1
    Last Post: September 29th 2006, 07:22 AM

Search Tags


/mathhelpforum @mathhelpforum