Statistics - M/C

posted by .

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 higher?

a. 68.7 b. 71.5 c. 73.2 d. 74.6 e.69.9

The answer is E, but don't know why.



2. Suppose the test scores of 600 students are normally distributed with a mean of 76 and variance
of 64. The number of students scoring between 70 and 82 is:

a. 272 b. 164 c. 260 d. 136 e. 328

The answer is E but don't know why.

  • Statistics - M/C -

    14. Variance = SD^2

    Z = (score-mean)/SD = (score-62)/15

    Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion (.30) to give you the Z score. Put that value in the above equation to find the score.

    Z = ([70 or 82]-76)/8

    Use the Z scores in the same table to find the proportions between them and multiply by 600.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. business statistics

    Your statistics instructor wants you to determine a confindence interval estimate for the mean test score for the next exam. In the past, the test scores have been normally distributed with a mean of 74.2 and a standard deviation of …
  2. statistics

    Scores on a certain test are normally distributed with a variance of 14. A researcher wishes to estimate the mean score achieved by all adults on the test. Find the sample size needed to assure with 95% confidence that the sample mean …
  3. statistics

    In one history class, 34 students took an exam. The mean of the exam was 52 with a standard deviation of 13. If the instructor is going to assume data are normally distributed and assign grades on a curve, then she will assign an A …
  4. statistics

    Scores on a certain test are normally distributed with a variance of 91. A researcher wishes to estimate the mean score achieved by all adults on the test. Find the sample size needed to assure with 95.44 percent confidence that the …
  5. statistics

    The scores on an economics examination are normally distributed with a mean of 66 and a standard deviation of 14. If the instructor wishes to assign a grade of A to the top 10% of the class, what is the lowest score a student may have …
  6. Statistics

    The marks of 100 students in an examination are normally distributed with mean of 25 marks and a standard deviation of 10 marks. (a) Given that the pass mark is 20, estimate the number of students who passed the examination. (b) If …
  7. statistics

    the marks of 100 students in an examination are normally distributed with mean of 25 marks and a standard deviation of 10 marks. Given that the pass mark is 20, estimate the number of students who passed the examination.
  8. Ib math

    The marks of 2376 students in an IB exam are normally distributed with mean 49 marks and variance 225 A) if the mark is 45 estimate the number of candidates who passed the exam?
  9. statistics

    the marks of 100 students in an examination are normally distributed with mean of 25 marks and a standard deviation of 10 marks. Given that the pass mark is 20, estimate the number of students who passed the examination.
  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