Results 1 to 7 of 7

Math Help - Stumped again!! Statistics... :(

  1. #1
    Junior Member
    Joined
    Apr 2006
    Posts
    39

    Exclamation Stumped again!! Statistics... :(

    Hi guys!

    THanks for all your help guys - esp Mr F!

    I am stumped on these 2 questions! Any one have any idea on how to proceed?




    Assuming the standard deviation for the cost of a bathroom remodel is known to be $545. How large a sample would need to be taken to estimate the mean cost of a bathroom remodel to within $136 with 99% confidence? I got 107 as my answer.


    A researcher is interested in estimating the proportion of employees who are unhappy in their current. A prior study estimates this proportion at 0.13. How large a sample would need to be taken to estimate this proportion to within 4% with 95% accuracy? i got 71 as my answer

    any help would be appreciated!

    Cheers

    Sunny
    Last edited by darren_a1; April 4th 2008 at 04:35 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Eater of Worlds
    galactus's Avatar
    Joined
    Jul 2006
    From
    Chaneysville, PA
    Posts
    3,001
    Thanks
    1
    The first one is correct. The second one(proportion) should be 272 as the minimum sample size.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Apr 2006
    Posts
    39
    Quote Originally Posted by galactus View Post
    The first one is correct. The second one(proportion) should be 272 as the minimum sample size.
    How do you come up with 272?

    Cheers

    darren
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Eater of Worlds
    galactus's Avatar
    Joined
    Jul 2006
    From
    Chaneysville, PA
    Posts
    3,001
    Thanks
    1
    I ran it through my Excel Stats sheet I use for this stuff.

    But, here is the 'old-fashioned' way:

    n=pq(\frac{z}{E})^{2}

    p=.13, q=.87, z=1.96, E=.04

    n=(.13)(.87)(\frac{1.96}{.04})^{2}=271.55=272
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Apr 2006
    Posts
    39

    here is what i did!

    he z value for the 95% interval is 1.96.

    The interval for a proportion is:

    mean - sqrt(p(1-p)/N) to mean + sqrt(p(1-p)/N)

    We want the sqrt(p(1-p)/N) to be 0.04:

    0.04 = sqrt(p(1-p)/N)

    p = 0.13

    0.04 = sqrt(0.13*0.87/N)

    0.04 = sqrt(0.1131/N)

    Square:

    0.1131/N = 0.0016

    Multiply:

    0.0016N = 0.1131

    Divide:

    N = 0.1131/0.0016

    N = 70.6875

    Round up:

    N = 71
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Eater of Worlds
    galactus's Avatar
    Joined
    Jul 2006
    From
    Chaneysville, PA
    Posts
    3,001
    Thanks
    1
    The formula for sample size in proprotions is as I gave you:

    n=pq(\frac{z}{E})^{2}

    Run it through a calculator. I bet you get 272. I checked this with Excel and my TI-92
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member
    Joined
    Apr 2006
    Posts
    39
    ok!

    Thanks for the help! could u look at the other post that i just got going?

    cheers


    Darren
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] Stumped... cosθ=sin(90-θ)
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: July 24th 2010, 01:17 PM
  2. Help, I'm stumped!
    Posted in the Geometry Forum
    Replies: 2
    Last Post: September 11th 2009, 07:44 AM
  3. Stumped
    Posted in the Algebra Forum
    Replies: 1
    Last Post: September 9th 2008, 05:38 PM
  4. I'm stumped. Please help.
    Posted in the Algebra Forum
    Replies: 1
    Last Post: February 26th 2008, 02:51 AM
  5. Wow... I am stumped!
    Posted in the Algebra Forum
    Replies: 2
    Last Post: March 28th 2007, 09:55 AM

Search Tags


/mathhelpforum @mathhelpforum