Business 101

Sample Problem

A random sample of 10 shoe sizes was taken in a classroom. Each person’s shoe size was measured with a very accurate ruler. The results in shoe sizes were:

5, 6, 6.5, 7, 7.5, 8, 8, 8.5, 9, 9.5

(b) What sample size would be necessary to estimate the true size with an error of +/- 0.03 inches with a 90 percent confidence?

To answer this problem, you need to do the following:

1. Find the Standard Deviation for the shoe sizes listed above using Megastat or Easy Calculation.com

2. Click on the "Megastat" menu option in Excel.

3. Click on "Confidence Intervals/Sample Size."

4. Choose a sample size calculation you'd like to perform by clicking on one of the tabs on the left hand side of the pop up window; Click on "Sample Size - mean."

5. Type your Standard Error into the "E" box, then type your Standard Deviation into the "Std. Dev." text box.

6. Select 90% in the “Confidence Level” drop down menu, then click on "OK." Megastat will return the appropriate sample size.

7. The answer is the number in the “Rounded Up” row (last row)

Problem Solution

5, 6, 6.5, 7, 7.5, 8, 8, 8.5, 9, 9.5 = Mean of 7.5

Standard Error of +/- of .03

1. Find the Standard Deviation for the shoe sizes listed above using Megastat or Easy Calculation.com = 1.394

2. Click on Megastats

3. Click on "Confidence Intervals/Sample Size."

4. Click on "Sample Size - mean" on the left hand side of the pop up window.

5. Type your Standard Error into the "E" box. = .03

6. Type your Standard Deviation into the "Std. Dev." text box. = 1.394

7. Select 90% in the “Confidence Level” drop down menu.

8. Click on "OK." Megastat will return the appropriate sample size.

9. The answer is the number in the “Rounded Up” row (last row)

Answer is 5842 (Number in last row)