From historical data, you know that the time it takes to do a certain job is normally distributed with a mean of 130 minutes and a standard deviation of 20 minutes. To monitor performance, each week a sample of 25 jobs is selected, and the average time it takes to do the job is recorded. In a particular week, the average time to do the job was 128 minutes with a standard deviation of 16 minutes. The distribution of times in the sample comes out bell-shaped. What can you say, if anything, about each of the following intervals?
a) 128 +/- 2 * 16
b) 130 +/- 2 * (20 / √25)
c) 128 +/- 2 * (16 / √25)
b) 128 +/- 2 * (20 / √25)