Results 1 to 3 of 3

Math Help - Standard Devitation Help

  1. #1
    Newbie
    Joined
    Feb 2008
    Posts
    4

    Standard Devitation Help

    Hello again,
    I have three questions here based on standard deviation that I either don't understand or am don't understanding key concepts.
    The first question is a word problem:

    "When reporting results to head office, Janice was told to make sure that the mean is 100 and the standard deviation is 10. When she calculated these statistical measures, she found the actual standard deviation to be 8.4 and the mean to be 106.5. Explain what Janice has to do before sending in her results to head office"
    Here I just don't understand what could be done, and it makes me want to smash my head into the wall just like that guy.


    "Krina works in a call center assisting home-computer users. The average length of a call in her center is 605 seconds. Her last call took only 569 seconds. her manager offers a bonus for calls that are handled efficiently and quickly. If a call is hand;ed more quickly than 95% of calls, a $2 bonus is paid. What is the largest standard deviation for calls that would let Krina's latest call get the bonus? " I don't even know where to begin with this question.

    The third and final question is:
    "A biology teacher recorded the lung capacity of each 16-year-old in her school. The teacher determined that the values were normally distributed with a mean of 3500 mL and a standard deviation of 300 mL. If 23% of the 16-year-olds lung capacities were less than Samantha's, what is Samantha's lung capacity?"
    I think I know how to answer it, but every time I try I end up with some absurd number.

    Thanks for help with any of these in advance.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by Fishsticks View Post
    Hello again,
    I have three questions here based on standard deviation that I either don't understand or am don't understanding key concepts.
    The first question is a word problem:

    "When reporting results to head office, Janice was told to make sure that the mean is 100 and the standard deviation is 10. When she calculated these statistical measures, she found the actual standard deviation to be 8.4 and the mean to be 106.5. Explain what Janice has to do before sending in her results to head office"
    Here I just don't understand what could be done, and it makes me want to smash my head into the wall just like that guy.
    You are going to modify the marks to have mean 100 and SD 10, this is the equvalent of marking an exam on a curve.

    Let x_i,\ i=1, 2, ..., n be the results, then the normalised results are:

     <br />
y_i=100+(x_i-106.5)(10/8.4)<br />

    The idea is that x_i-106.5 has mean 0 and SD 8.4, so (x_i-106.5)(10/8.4) has mean 0 and SD 10, so y_i has mean 100 and SD 10.

    RonL
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Feb 2008
    Posts
    4
    Thank you very much for that, sir, cheers.
    I am going to take another good stab at the other questions tomorrow. I'm sure I'm going to come up with a feasible solution right when I'm about to fall asleep and have to try it again.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: March 10th 2011, 01:39 PM
  2. Replies: 5
    Last Post: May 18th 2009, 04:14 AM
  3. Replies: 0
    Last Post: October 23rd 2008, 08:03 AM
  4. standard
    Posted in the Statistics Forum
    Replies: 2
    Last Post: March 24th 2008, 06:56 AM
  5. standard dev
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: April 24th 2006, 04:04 PM

Search Tags


/mathhelpforum @mathhelpforum