Question

2. If the data represent all customers visiting one of the Pelican store in a day a. Estimate a 97% confidence interval estimate for the age of customers. b. Estimate a 96% confidence interval estimate of the proportional of customers who paid by the Proprietary Card.

Answer 1

There is no data given in the question. So what I would do is to explain how to get confidence interval for any data. That way it should be pretty easy to calculate the Confidence Intervals.

Please see the image below for the process-

Now that you have all the values, all you need to do is to plug them in into the formula for Confidence Interval.

Of course, calculating standard deviation by hand or calculator is difficult. Use Microsoft Excel for that. Just enter this formula-

=stdev(X₁,X₂,.....X_n), where X₁ etc is your population.

Alternatively, use this link to calculate standard deviation- http://www.calculator.net/standard-deviation-calculator.html

Also, this is the way you read a z-table. (link- http://www.statisticshowto.com/tables/z-table/)

You see what your value is. In part A of our question, it came to be .485. You then see where this value is in the table. For us, its at the intersection of 2.1 and .07. Then you add these 2 values to get the z-value. For us it turns out to be 2.17. So, for us the confidence interval would be-

(mean of the population)+2.17*()