The Results of a Wagner Turbidity Test Performed on 15

Essay

The results of a Wagner turbidity test performed on 15 samples of standard Ottawa testing sand were (in microamperes) $\begin{array} { l l l l l l l l } 26.9 & 25.8 & 24.4 & 24.1 & 26.4 & 25.9 & 24.0 & 21.7 \\24.9 & 25.9 & 27.3 & 26.7 & 26.9 & 24.8 & 27.3 &\end{array}$
a. Is it plausible that this sample was selected from a normal population distribution?
b. Calculate an upper confidence bound with confidence level 90% for the population standard deviation of turbidity.