A random sample of 42 college graduates revealed that they worked an average of 5.5 years on the job before being promoted. The sample standard deviation was 1.1 years. Using the 0.99 degree of confidence, what is the confidence interval for the population mean?

Confidence interval for the population mean = 5.063 to 5.937

Explanation:

For confidence interval for the population mean you first need to calculate error. For Error, E = z value * sample standard deviation / sq. root of sample.

z value for 99% confidence = 2.58

Sample standard deviation = 1.1

Sq. root of sample = sq. root of 42 = 6.4807

E = 2.58 * 1.1/6.4807 = 0.4371

Now, confidence interval (CI) = Mean + / - Error

CI = 5.5 + / - 0.4371 which gives 5.063 to 5.937