Results 1 to 2 of 2

Math Help - Help with normal distribution

  1. #1
    Newbie
    Joined
    Nov 2012
    From
    Toronto
    Posts
    2

    Help with normal distribution

    Daily sales in a store follows a normal distribution with mean $2000 and standard deviation $500. Suppose daily sales are independent from day to day.

    a) In the next 3 days, the probability that daily sales exceed $2000 in at least two days is ______.
    b) In the next 9 days, the probability that the average daily sales is over $1800 is ______.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Sep 2012
    From
    Australia
    Posts
    3,651
    Thanks
    602

    Re: Help with normal distribution

    Hey alb41192.

    The sum of independent normal distributions are normally distributed with the means added up and the variances added up.

    So for three days you have a mean of 3*mu and a variance of 3*sigma^2.

    This means you are looking at Z ~ (X - 3*mu)/SQRT(3*sigma^2).

    Now this is for X1 = 3Y where this is for three days. If you want to do this for two days then you need to use X2 = 2Y.

    The probabilities are P(X1 > 2000 OR X3 > 2000) and P(X_bar > 1800).

    Recall that X_bar is equal to (X1 + X2 + ... + XN)/n which has mean mu and variance sigma^2/n.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. normal distribution prior and posterior distribution proof
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: March 9th 2011, 06:12 PM
  2. Replies: 1
    Last Post: October 18th 2010, 01:41 PM
  3. Replies: 2
    Last Post: March 29th 2010, 02:05 PM
  4. Replies: 2
    Last Post: August 25th 2009, 10:39 PM
  5. Replies: 1
    Last Post: April 20th 2008, 06:35 PM

Search Tags


/mathhelpforum @mathhelpforum