# Question- PERT

Submitted by sumedha82 on Tue, 09/13/2011 - 15:07

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. |

Forums:

bheemineni

Wed, 09/14/2011 - 02:22

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## Answer is “B” = 5.2 days

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

^{2}Project Standard deviation= √Sum of task Variances

Standard deviation of the allover path = √ [Var

A+ VarB+ VarC+ VarD+ VarE]=√[(24-12)/6^{2}+(14-8)/6^{2}+(27-15)/6^{2}+(28-10)/6^{2}+(35-17)/6^{2}]=√[2^{2}+ 1^{2}+ 2^{2}+3^{2}+3^{2}]=√ 27= 5.196Sorry if the symbols are not clear. I hope it still makes sense.

Vijay Bheemineni, MS, PMP, ITIL

RP

Wed, 09/14/2011 - 06:49

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## I despise Oliver Lehman's

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.

sumedha82

Wed, 09/14/2011 - 10:07

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## Thanks

Thanks Vijay for the detailed explanation.

Thanks RP for the heads-up.

pmalik

Fri, 09/22/2017 - 08:30

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## PERT

For help in answering your question you can read the following articles:

How to use PERT, CPM and Standard Deviation Together?

What is the Use of Standard Deviation?

3-Point Estimate is Different From PERT