Age at diagnosis for each of 20 patients under treatment for meningitis was given in the paper "Penicillin in the Treatment of Meningitis" (Journal of the American Medical Association [1984]: 1870-1874). The ages (in years) were as follows:
a. Calculate the values of the sample mean and the standard deviation.
b. Compute the upper quartile, the lower quartile, and the interquartile range.
c. Are there any mild or extreme outliers present in this data set?
d. Construct the boxplot for this data set.