# Statistics Question 3

**Question description**

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 x 16, (b) 130 ± 2 x (20/√25), (c) 128 ± 2 x (16/√25),
(d) 128 ± 2 x (20/√25).

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