Results 1 to 5 of 5

Math Help - Hard Problem

  1. #1
    Newbie
    Joined
    Apr 2005
    Posts
    8

    Question Hard Problem

    A sample of 40 families is taken, and a sample mean income of $44,000 with a sample standard deviation of $9,500 is calculated. Determine a 90% confidence interval for the population means income.

    a. $41,469, 46,531
    b. $41,529, $46,471
    c. $40,233, $45,887
    d. $45,676, $50,324
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Site Founder Math Help's Avatar
    Joined
    Apr 2005
    Posts
    171
    n = number of samples = 40

    = standard deviation = $9,500

    = mean = $44,000

    90% confidence interval = [ - 1.645/n, + 1.645/n]

    the number 1.645 from the above equation is looked up in a table or in a calculator I can show you how to do this if you need it.

    Therefore the interval is 44,000 plus or minus (1.645*9,500/40) somewhow I am not getting an answer in your list . . . can anyone help?
    Attached Thumbnails Attached Thumbnails Hard Problem-zpic1.gif  
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Apr 2005
    Posts
    35
    Are you using t-values or z-values??
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Site Founder Math Help's Avatar
    Joined
    Apr 2005
    Posts
    171
    I forgot the square root.

    n = number of samples = 40
    = standard deviation = $9,500
    = mean = $44,000

    90% confidence interval = [ - 1.645/n, + 1.645/n]

    the number 1.645 from the above equation is looked up in a table or in a calculator I can show you how to do this if you need it.

    Therefore the interval is 44,000 plus or minus (1.645*9,500/sqrt(40))
    this gives: b. $41,529, $46,471 as the answer.
    Last edited by Math Help; April 21st 2005 at 10:07 PM.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Apr 2005
    Posts
    8

    Thanks

    You saved the day
    Follow Math Help Forum on Facebook and Google+


Similar Math Help Forum Discussions

  1. A really hard problem!
    Posted in the Math Puzzles Forum
    Replies: 3
    Last Post: September 8th 2009, 12:51 PM
  2. hard problem
    Posted in the Algebra Forum
    Replies: 1
    Last Post: February 19th 2009, 02:40 AM
  3. Help Now Please hard problem!!!
    Posted in the Statistics Forum
    Replies: 1
    Last Post: December 11th 2007, 07:28 AM
  4. This Alg 2 problem is hard
    Posted in the Algebra Forum
    Replies: 1
    Last Post: April 8th 2007, 10:48 PM
  5. Very hard age problem...
    Posted in the Algebra Forum
    Replies: 2
    Last Post: October 1st 2006, 08:18 AM

Search Tags


/mathhelpforum @mathhelpforum