In a genetic study, a regular food was placed in each of 20 vials and the number of flies of a particular genotype feeding on each vial recorded. The counts of flies were also recorded for another set of 20 vials that contained grape juice. The following data sets were obtained

(courtesy of C. Denniston and J. Mitchell).

No. of Flies (Regular Food)

15 20 31 16 22 22 23 33 38 28 25 20 21 23 29 26 40 20 19 31 No. of Flies (Grape Juice)

6 19 0 2 11 12 13 12 5 16 2 7 13 20 18 19 19 9 9 9

(a) Plot separate dot diagrams for the two data sets.

(b) Make a visual comparison of the two distributions with respect to their centers and spreads.

(c) Calculate and s for each data set.