In the previous problem, a second proposal has been made to reduce the purging time of 3.5 hours during a changeover to less than 1.5 hours by sequencing the batches of parts so as to reduce the differences in plastic type and color between one part and the next. In the ideal, the same plastic can be used for all parts, thus eliminating the necessity to purge the injection barrel between batches. Thus, the limiting task in changing over the machine is the mold change time, which is 1.5 hours. For the 1.5-hour setup, determine
(a) The economic batch quantity,
(b) The total number of hours per year that the injection-molding machine is down for changeovers, and
(c) The annual inventory cost.