Question: (pg. 355) 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 other following intervals:

1. 128±2×16
2. 130±2×(20/ )
3. 128±2× (16/ )
4. 128±2×(20/ )

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