Leveling solution

The Gantt chart is shown here.  The critical path is ACEI and expected project duration is 21 weeks. Of course this assumes all needed resources are available.  gannt-chart-for-leveling,  The resources diagram is also shown here resource-diagram (from Excel) and from MS Projectleveling-original
From the resource diagram, it is obvious the project is over-allocated if there are only 10 engineers available. The over-allocation occurs between  weeks 7-14. Thus, to remove the over-allocation we need to move some of the activities being performed in weeks 7-14 out of that period.  What tasks should be moved?  To protect the critical path, one option is to move tasks with slack, perhaps starting with the one with the most slack first. Of course there are rules that could be used and some of these are mentioned in the test book.
Here are the tasks being done in weeks 7-14 that have slack:  D, H, G &J. So we could delay D until C is finished. That means D will after week 10 and finish after week 13.  This action will require that G starts after 13 and finish 18.  This means then that we will doing E, G, J together for some time and the total number of engineers required for the three tasks exceeds 10.  So, some other tasks will have to be moved again. Working through this iterative will show that it is not possible to meet the 21 week schedule if you only have 10 engineers.  Confirm for yourself that it will take 28 weeks for that level of resources. See the leveled diagram here leveled-10-engineers
What about if management could increase the number of engineers to 12?  Going through this exercise again, we will notice this time  that the over-allocation occurs only between weeks 11-14. It is still not possible to finish within 21 weeks. However, if for example, we move G  to weeks 19-24 (after J is finished) and move I (24-25), the project can finished in 25 weeks. Confirm for yourself that a better alternative is to move J and finish in 24 weeks. see MS project chart here leveled-12-engineers
So to conclude, the project manager could go to management with three scenarios:
1. with only 10 engineers the project will take 29 weeks.
2. with 12 engineers, it will take 24 weeks.
3. to finish in 21 weeks will require 14 engineers.
The above analysis assumes tasks cannot be split.
Here is you turn to practice the above concepts with this example. Resource-leveling-Practice-Problem
Check your answer here Leveling-solution
One last point; you will notice that the original critical paths in the examples done here were no longer valid when you are resource constrained. Further, projects require different types of resources so removing the overallocation for one resource creates problems for another resource. This makes managing resource constrained projects very difficult. This leads us into the next concepts on critical chain project management.