Five Strains of the Staphylococcus Aureus Bacteria Were Grown at 35

Multiple Choice

Five strains of the Staphylococcus aureus bacteria were grown at 35 degrees Celsius for 24 hours in a culture broth containing either 0.6% of the nutrient tryptone or 1% of tryptone. We want to know if these two tryptone concentrations affect the growth of S. aureus in culture. Here are the resulting bacterial counts for each condition and bacterial strain: $$\begin{array} { l l l l l l } & \text { Strain 1 } & \text { Strain 2 } & \text { Strain3 } & \text { Strain 4 } & \text { Strain 5 } \\\mathbf { 0 . 6 \% } \% \text { tryptone } & 66 & 71 & 93 & 102 & 62 \\\mathbf { 1 } \% \text { tryptone } & 147 & 63 & 89 & 106 & 98\end{array}$$
We choose to analyze these data using the Wilcoxon signed rank test.
If the bacterial counts have a continuous distribution that is not affected by the different treatments, what is the standard deviation of the Wilcoxon signed rank test statistic, W⁺?

A) 3.71
B) 4.50
C) 7.50
D) 13.75