Question

The following are the midterm exam grades (in %) of a simple random sample of 39 statistical students:

85 64 45 77 53 72 99 59 68 92 48 75 51 93 67 78 89 56 83 71 49 94 63 77 79 88 42 65 92 69 73 56 81 69 61 75 58 67 81

a). make a 75% confidence statement about the mean grade of all statistical students on a similar midterm

b). what is the sample proportion of the statistical students who scored more than 60% on this midterm exam?

c). make a 99.9% confidence statement about the proportion of all statistical students who would score more than 60% on a similar midterm

d) Which of the following would make the confidence interval you have calculated in part g) narrower? Which of the following would make it wider? Which of the following would have little effect on the interval?

• ·  if you created a 68% conf. interval instead of the 99.9% conf. interval ...........................................................
• ·  if you had a SRS of 2 student results instead of the 39 you have now...............................................................
• ·  if the population of all statistical students was twice as big as it is nowadays..................................................

Answer 1

If a 68% confidence interval was constructed instead if 99.9%, then the interval would become narrow.

If the SRS is of size 2 instead of 39, then the interval would widen.

If the population was twice as big as it is nowadays, interval would remain unaffected.