Alexander Demetrius Dickson, ADD to his friends, has three big projects he is working on, and he can't seem to organize his time effectively. Each of the three projects, we'll call them A, B, and C, should take ten days to complete

He is currently contemplating two different approaches. Approach one is to work each project to completion before starting on the next. The problem with this approach is that he tends to burn out if he works on one task for an extended period of time. For every two days he works on one single task, he finds he must take a half day off. ADD's alternative is to multitask, that is, work on project A for a day, then switch to project B for a day, before switching to project C for a day. The problem with this approach is that there is a small setup time equaling one-quarter of a day associated with each transition. Use a Gantt chart to show the effect of each approach and determine which method is the best (has the overall fastest completion time) for performing this work.

The actual task time and idle time are identical, the projects require 10 days each and there is a total of 7.5 days of setup (or burnout) time in each schedule. The top Gantt chart shows the effect of working straight through each project until completion. The total project time is ten days and the inserted idle time due to burnout is two days (shaded bars denote this rest period). The span of project A is twelve days. This would be followed by a rest period of a half day and then a similar pattern for project B. The final burnout day need not be considered (unless more projects follow) so the total time would be 37 days.

Multitasking appears as follows: times indicated on the timeline mark the end of the setup, so the 1.25 is one day of work on Project A followed by a one-quarter day setup, the 2.5 is the completion of the setup after the first day on Project B, and so on. It will take five iterations of the Gantt chart shown to complete all segments of projects A, B, and C, so the total time is 5×7.5=37.5, less the final quarter-day setup for a total time of 37.25 days; virtually the same as the above Gantt chart in terms of completion. The big difference is in the span of the jobs.

The big difference is in the span of the projects from their beginning to completion. The first schedule shows that Project A ends twelve days after it was begun. The same would hold true for projects B and C. For the second approach, project A ends 34.75 days after it was started, as do projects B and C.