A Small, Independent Amusement Park Collects Data on the Number

Essay

A small, independent amusement park collects data on the number of cars with out-of-state license plates. The sample size is fixed at n=25 each day. Data from the previous 10 days indicate the following number of out-of-state license plates:
$$\begin{array} { | c | c | } \hline \text { Day } & \begin{array} { c } \text { Out-of-state } \\\text { Plates }\end{array} \\\hline 1 & 6 \\\hline 2 & 4 \\\hline 3 & 5 \\\hline 4 & 7 \\\hline 5 & 8 \\\hline 6 & 3 \\\hline 7 & 4 \\\hline 8 & 5 \\\hline 9 & 3 \\\hline 10 & 11 \\\hline\end{array}$$
(a) Calculate the overall proportion of "tourists" (cars with out-of-state plates) and the standard deviation of proportions.
(b) Using ± 3σ limits, calculate the LCL and UCL for these data.
(c) Is the process under control?
Explain.