Results 1 to 4 of 4

Math Help - probability question

  1. #1
    Newbie
    Joined
    Oct 2009
    Posts
    19

    probability question

    I am studying for a test, and came across this question wondering if anyone can help me solve this.

    Neverready batteries lifetime is normally distributed. For a new type introduced for CD players, it was observed that the mean lifetie was 10.5 hours, and 90% lasted longer than 9 hours. If you take a random sample of 4 batteries, what is the probability that exactly 2 lasted longer than 11 hours?

    thank you very much.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by shellshock View Post
    I am studying for a test, and came across this question wondering if anyone can help me solve this.

    Neverready batteries lifetime is normally distributed. For a new type introduced for CD players, it was observed that the mean lifetie was 10.5 hours, and 90% lasted longer than 9 hours. If you take a random sample of 4 batteries, what is the probability that exactly 2 lasted longer than 11 hours?

    thank you very much.
    First find the variance of X (the lifetime of a battery) using the given information.

    Then calculate p = Pr(X > 11).

    If Y is the random variable 'number of batteries that last longer than 11 hours' then Y ~ Binomial(n = 4, p = as above).

    Calculate Pr(Y = 2).
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Oct 2009
    Posts
    19
    Quote Originally Posted by mr fantastic View Post
    First find the variance of X (the lifetime of a battery) using the given information.

    Then calculate p = Pr(X > 11).

    If Y is the random variable 'number of batteries that last longer than 11 hours' then Y ~ Binomial(n = 4, p = as above).

    Calculate Pr(Y = 2).
    I'm sorry , can you show me how to find the variance?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by shellshock View Post
    I'm sorry , can you show me how to find the variance?
    Read this thread: http://www.mathhelpforum.com/math-he...lp-please.html
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 5
    Last Post: February 10th 2013, 02:11 PM
  2. Probability question
    Posted in the Statistics Forum
    Replies: 3
    Last Post: March 10th 2010, 01:45 PM
  3. Probability Question
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: December 25th 2009, 02:56 AM
  4. Probability question involving (A given B type question )
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: November 9th 2009, 09:08 AM
  5. A probability question and an Expectations question
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: January 29th 2006, 06:13 PM

Search Tags


/mathhelpforum @mathhelpforum