The Professor's Response

I had a question on 7.2 Number 20:

20. A survey of thirty-one, 2005 Major League Baseball salaries for pitchers playing in the National

League had a mean of $2,522,785 and a standard deviation of $4,065,579. Construct the 98%

confidence interval for the true average salary for all NLMLB pitchers in 2005.

I was slightly off, I got (2655766.8, 238903.2) I tried to review it, but my answer was still wrong The same thing happened when I did the other similar problems about the baseball player.

See the professor's answer below.

Hi Natalie,

You wrote that your answer is only slightly off, but your answer is very different from the one that is correct for this problem. Also, you need to be careful to write your interval in the correct order. The smaller number must always be the first value in the interval (the number on the left).

I have created a video to explain how this problem is done. In this problem the sample values (the mean and standard deviation) are large numbers. You want to make sure you do not round before the end when working with values this large. If you do any rounding up front, it will show up more noticeably when working with large values.

Also, make sure you are using the t-table here to find the critical value in step two because it provides an extra decimal place of accuracy. If you use the z-table, you will again have more rounding error which will show up noticeably with such large values.

Hope that helps,

Professor McGuckian