A study of 60 professors showed that the time they spent on the average in creating test questions was 17.0 minutes per question. The standard deviation of the population is 2. Which of the following is the 98% confidence interval for the average number of minutes it takes to create a test question?
A) (15.99, 18.01)
B) (16.58, 17.42)
C) (16.40, 17.60)
D) (12.35, 21.65)

Question

Quizplus · Accepted Answer

We can use the formula for a confidence interval:
CI = x̄ ± z*(σ/√n)
where x̄ = 17, σ = 2, n = 60, and z for a 98% confidence interval is 2.33
Plugging in these values, we get:
CI = 17 ± 2.33*(2/√60)
CI = (16.40, 17.60)
Therefore, the best choice is C.

A Study of 60 Professors Showed That the Time They