Results 1 to 4 of 4

Math Help - Can any one help with Normal Distribution. dont have much time left!!

  1. #1
    Newbie
    Joined
    Mar 2008
    Posts
    2

    Exclamation Can any one help with Normal Distribution. dont have much time left!!

    i have a last Q left to do for my maths coursework and it has completely stumped me. can anyone help. here is the whole Q:

    A scientist was measuring oak trees in a woodland and noticed that their height was normally distributed. Unfortunately a sudden gust of wind caught her by surprise and most of her results were blown away. All she had left was the knowledge that she measured the height of 200 oak trees and found that 12 trees were less than 8 metres tall and 36 trees were less than 10 metres tall.

    Fortunately the scientist knew the properties of normal distribution to work out the mean and standard deviation of the height of the oak trees. Do you?

    By sketching a graph of the normal distribution and indicating appropraite areas, determine the mean height of the oak trees and their standard deviation.

    If anyone can help quickly that would be great.

    Thanks
    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 wicca16 View Post
    i have a last Q left to do for my maths coursework and it has completely stumped me. can anyone help. here is the whole Q:

    A scientist was measuring oak trees in a woodland and noticed that their height was normally distributed. Unfortunately a sudden gust of wind caught her by surprise and most of her results were blown away. All she had left was the knowledge that she measured the height of 200 oak trees and found that 12 trees were less than 8 metres tall and 36 trees were less than 10 metres tall.

    Fortunately the scientist knew the properties of normal distribution to work out the mean and standard deviation of the height of the oak trees. Do you?

    By sketching a graph of the normal distribution and indicating appropraite areas, determine the mean height of the oak trees and their standard deviation.

    If anyone can help quickly that would be great.

    Thanks
    Pr(X < 8) = 12/200 = 0.06.

    Pr(X < 10) = 36/100 = 0.18.


    z_{0.06} = -1.5548

    z_{0.18} = -0.9154

    (correct to four decimal places).


    Z = \frac{X-\mu}{\sigma}. Therefore:

    -1.5548 = \frac{8-\mu}{\sigma} .... (1)

    -0.9154 = \frac{10-\mu}{\sigma} .... (2)


    Solve equations (1) and (2) simultaneously.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Mar 2008
    Posts
    2

    Exclamation help a bit more please!

    -0.5 = 8 - mue / s.d.

    8 - mue = -0.5

    B = 0.14 z= 0.0557

    0.0557 = 10 - mue / s.d.

    10 - mue = 0.0557

    0.0557 x 100 = 5.57

    dont know if this is right or not and we are quite stuck on how else to do it. could you help any more?
    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 wicca16 View Post
    -0.5 = 8 - mue / s.d.

    8 - mue = -0.5

    B = 0.14 z= 0.0557

    0.0557 = 10 - mue / s.d.

    10 - mue = 0.0557

    0.0557 x 100 = 5.57

    dont know if this is right or not and we are quite stuck on how else to do it. could you help any more?
    I have no idea what you've done here.

    And I have no inclination to explain why it's wrong - all I can see is that you've completely ignored the approach I suggested.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: August 1st 2011, 07:03 AM
  2. Time left equation
    Posted in the Math Topics Forum
    Replies: 0
    Last Post: July 15th 2010, 06:57 PM
  3. Replies: 2
    Last Post: March 29th 2010, 03:05 PM
  4. Normal Distribution life time of batteries
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: March 11th 2010, 06:49 PM
  5. Replies: 1
    Last Post: April 20th 2008, 07:35 PM

Search Tags


/mathhelpforum @mathhelpforum