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 the 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/- 2 *16

b)130 +2/- 2 * (20 / sqrt 25)

c)128 +2/- 2 * (16 / sqrt 25)

d)128 +2/- 2 * (20 /sqrt 25)