The following data are the ages (in years) at diagnosis for 20 patients under treatment for meningitis:

18 18 25 19 23 20 69 18 21 18

20 18 18 20 18 19 28 17 18 18

(a) Calculate and interpret the values of the sample mean, variance, and standard deviation.

(b)  Compute the 10% trimmed mean and the sample median. Why might you recommend either one of these two statistics as measures of center rather than the sample mean?

(c) Compute the upper quartile, the lower quartile, and the interquartile range.

(d)  Illustrate the center, spread, and symmetry or skewness of this data using a horizontal modified boxplot.