The city of Madison regularly checks the water quality at swimming beaches located on area lakes. The concentration of fecal coliforms, in number of colony forming units (CFU) per 100 ml of water, was measured on fifteen days during the summer at one beach.

180 1600 90 140 50 260 400 90 380 110 10 60 20 340 80

(a) Make a dot diagram.

(b) Comment on the pattern and any unusual features.

(c) The city closes any swimming beach if a count is over 1350. What proportion of days, among the fifteen, was this beach closed?