5-20 Generalize Model 5-4 to have two additional types of items (doodads and kon- traptions), as well as widgets; initially, there are 60 widgets, 50 doodads, and 70 kon- traptions. The customers arrive in the same pattern as before, but now each customer will have a demand for doodads and kontraptions, as well as for widgets. Widget demands are as before, doodad demands are POIS(1.9), and kontraption demands are POIS(2.3); assume that a customers demand for an item is independent of his or her demands for the other two items. Theres still one inventory evaluator, who still arrives at the beginning of each day, but now has to look at all three inventories and order according to separate (s, S) policies for each of the three inventories; you may clone this inventory evaluator for this triple duty, using two tandem instances of the Separate flowchart module. For widgets, (s, S) = (20, 40) as before; for doodads, (s, S) = (15, 35); and for kontraptions, (s, S) = (25, 45). Delivery lags for widgets are UNIF(0.5, 1.0) as before; for doodads, its UNIF(0.4, 0.8); and for kontraptions, its UNIF(0.8, 1.7); note that for kontraptions, its possible for a delivery lag to extend beyond the time of the next inven- tory evaluation, but make the order decision based on only the inventory on hand, rather than based on the inventory on hand plus on order (even though the latter might make more sense; see Exercise 5-25). Ordering costs (both setup and incremental), holding, and shortage costs for doodads and kontraptions are the same as for widgets. Run the simulation for the same length of time as Model 5-4 (that is, its okay to fudge the ending point to avoid useless inventory evaluations at time 120), and get the total daily cost, as well as separate holding and shortage costs for each type of item. Make separate Level (thermometer) and regular Plots for each of the three types of items in inven- tory. Describe how you would model this if you had hundreds or thousands of different kinds of items in inventory instead of just three.

5-21 In Exercise 5-20, suppose that the suppliers for the three items merge and offer a deal to eliminate multiple setup costs on a given days ordersthat is, if Bucky orders any items of any type at the beginning of a day, he only has to pay the $32 setup cost once for that day, not a separate $32 for each type of item he orders. (If no order is placed for anything, theres still no setup cost.) Modify your model for Exercise 5-20 to do this. What kind of incentives do you think this alternate cost structure might place on Bucky in terms of picking better values of s and S for each item (see Exercises 6-13 and 6-14)?