# Thread: Large Sample Confidence Interval for the Mean - Problem is it right ???

1. ## Large Sample Confidence Interval for the Mean - Problem is it right ???

The president of Jones Bank asked his research team to determine the average waiting time for its customer. A study of 100 customers was conducted with the following results: mean = 19.8 standard deviation = 2.06 minutes
Prepare the 95% confidence interval for average waiting time...

mean = 19.8
standard deviation = 2.06 minutes
sample / n = 100
95% confidence interval = 1.96

standard error = 2.06/sqrt 100 = 2.06/10 = .206

19.8 +/- 19.96 (.206)

19.8 +/- 0.40376

19.39 less than or equal to u less than or equal to 20.20

Jones Bank can be 95% confident that the average waiting time for customers is between 19.39 and 20.20

2. ## Re: Large Sample Confidence Interval for the Mean - Problem is it right ???

Seems right. You have some typos and the true definition of CI is a little different from what you have.

I would write:

Jones bank average wait time is 19.8 (95% CI: 19.39, 20.20).

3. ## Re: Large Sample Confidence Interval for the Mean - Problem is it right ???

However,
Jones Bank should be made aware that waiting times are generally left skewed, so the mean might not be a good measure....

4. ## Re: Large Sample Confidence Interval for the Mean - Problem is it right ???

Thanks so much for answering my questions I am so grateful for your help...

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