Demand for jelly doughnuts on Saturdays at Don's Doughnut Shoppe is shown in the following table. Determine the optimal number of doughnuts, in dozens, to stock if labor, materials, and overhead are estimated to be $3.20 per dozen, doughnuts are sold for $4.80 per dozen, and leftover doughnuts at the end of each day are sold the next day at half price. What is the resulting service level?
Demand {dozens} Relative Frequency
19 .01
20 .05
21 .12
22 .18
23 .13
24 .14
25 .10
26 .11
27 .10
28 .04
29 .02