:3a. Solution. The SD of the error box is unknown, so we use the t-distribution. The sample average is
15+17/2 = 16 .
The SD of the sample is 1. The SD+ of the sample is the square root of 2. The SE of the sum of the measurements is estimated by
the square root of 2 x the square root of 2 = 2.
The SE of the average of the measurements is 2/2 = 1. We use the t-distribution with 2-1 = 1 degrees of freedom. The appropriate multiplier is 12.71, so a 95% confidence interval is given by
16 +/ 12.71x1 ,
or (approximately) from 3 to 29.