Asample of 25 different payroll departments found that the employees worked an average of 310.3 days a year with a standard deviation of 23.8 days.
what is the 90% confidence interval for the average days worked by employees in all payroll departments?
a. 301.0 < < 319.6
b. 298.0 < < 322.6
c. 302.2 < < 318.4
d. 314.1 < < 316.8

the average daus worked ny employees is C. 302.2 < < 318.4

Explanation:

Hi, since we need the 90% confidence interval, we have to cut 5% in both sides of the normal distribution graph (which accounts for 100%), therefore, the formula to use for both, the upper and lower limit of the interval is as follows.

Where 1.65 is the Z-score for the probability=0.05 and -1.65 is the Z-score for the probability = 95%

So, things should look like this

Therefore, the interval is 302.4 << 318.2 and since it is close to answer C. we selected answer C.

Best of luck.

answerblank(1) negatively.blank(2); rises; blank(3) falls;