Question- PERT

Another question from oliver.....Pls help (Apologies for the format)


A project manager made 3-point estimates on a critical path and found the following results:

Assuming ±3 Sigma precision level for each estimate, what is the standard deviation of the allover path?
  App. 4.2 days
  App. 5.2 days
  App. 6.2 days
  You can not derive the path standard deviation from the information given.

Task Variance = [(P-O)/6]2

Project Standard deviation= √Sum of task Variances

Standard deviation of the allover path = √ [Var A + Var B + Var C + Var D + Var E]

                        = [(24-12)/6 2+ (14-8)/6 2+ (27-15)/6 2+ (28-10)/6 2 + (35-17)/6 2]

                        = [22+ 12+ 22+32+32]

                        = √ 27 = 5.196

Sorry if the symbols are not clear. I hope it still makes sense.

Vijay Bheemineni, MS, PMP, ITIL

RP's picture

I despise Oliver Lehman's questions a whole lot. Did it during my prep but felt that during the actual exam, it was a serious waste of my time. If its anything to go by, you will not get such questions that require such detailed calculations. I have liaised with other colleagues and from our point of view, Oliver's questions just don't have any applicability to the actual exam.

Thanks Vijay for the detailed explanation.

Thanks RP for the heads-up.