Statistics

posted by .

Suppose X is a normally distributed random variable with the mean u(Mu) and variance sigma^2. Suppose P(X </= 10) - .6915 and P (X </= 20) -.8413. Find Mu and Sigma^2.

PLEASE HELP! THIS IS AN EXAM REVIEW QUESTION!

  • Statistics -

    for z-scores,
    z = (x - m)/s

    from my charts, a prob of .6915 corresponds to a z-score of .5
    so .5 = (10 - m)/s
    .5s = 10-m
    m = 10 - .5s

    and a prob of .8413 corresponds to a z-score of .9998 or 1
    1 = (20-m)/s
    s= 20-m
    m = 20 - s

    then 20 - s = 10 - .5s
    s = -10/-.5 = 20
    m = 0

    If I recall variance is the square of the standard deviation.

    I checked my answers with

    http://davidmlane.com/hyperstat/z_table.html

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Statistics

    Suppose that the fit to the simple linear regression of Y on X from 6 observations produces the following residuals: -3.3, 2.1, -4.0, -1.5, 5.1, 1.6. a) What is the estimate of sigma squared?
  2. statistics

    Suppose that you got a score of X=78 on an English test for which the mean was (mu)=70 and the standard deviation was (lower case sigma)=10. Also, suppose that you got a scores of X=64 on a Spanish test with mean(mu)=50 and (lower …
  3. Business statistics

    1(a)Let Y have a binomial distribution with parameters n and p. We reject Ho: p=1/2 and accept H1: p>1/2 if Y>=c. Find n and c such that the probability of a Type I error is .10, and P(reject Ho/p=2/3)=.95. (b)What is the probability …
  4. Statistics - M/C

    14. The marks on a statistics test are normally distributed with a mean of 62 and a variance of 225. If the instructor wishes to assign B’s or higher to the top 30% of the students in the class, what mark is required to get a B or …
  5. statistics

    a simple random sample will be obtained from a normally distributed population. find the minimum sample size needed to be 95% confident that the sample standard deviation (s) is within 10% of sigma. please help!
  6. statistics

    Suppose a random sample of 25 students is selected from a community college where the scores in the final exam (out of 125 points) are normally distributed, with mean equal to 112 and standard deviation equal to 12. Find the probability …
  7. statistics

    Suppose that the test scores for a college entrance exam are normally distributed with a mean of 450 and a standard deviation of 100. If a student is selected at random what is the probability that the student will score above 600?
  8. statistics

    Suppose the average body temp is 98.6 assume the variable is normally distributed with a standard deviation of .74 degrees. suppose a sample of 100 is taken. what is the probability that the mean is below 98.4?
  9. Statistics

    In a population, heights of males are normally distributed with u=180 cm and sigma^2=16 cm^2, while the heights of females are normally distributed with u=170 cm and sigma^2= 25 cm^2. a) One random male and one random female are selected …
  10. Statistics

    In a certain population the heights of men are normally distributed with mean 168.75 and variance 42.25 those of women are normally distributed with mean 162.50 and variance 36 the probability that the mean height of a random sample …

More Similar Questions