Standard Dev question

Submitted by Magnolia on Tue, 02/25/2014 - 00:03

Friends - Can someone guide me on this question, found this on one of the free PMP practice test - 

A project manager has been asked by the client to meet the promise date of the project. The project manager analyzes the schedule before promising a date to the customer. The project manager uses the program evaluation and review technique to evaluate the project schedule. She decides that based on the PERT calculations she can promise a delivery date of June 30. The expected value of the project completion date is May 30. If the project manager is willing to accept a 5% probability that the project will be delivered later than June 30, what is the standard deviation of the duration of the activities on the critical path? Assume a five-day workweek.

 

a. Ten days
b. Fifteen days
c. One-half month
d. One month

The right choice is C. Tried solving it myself but unable to get to it, also the test answer sheet did not have this question solved.

Thanks

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interservicio

Mon, 03/03/2014 - 12:02

For solving that one, you must use your SIGMA knowledge.

The question is telling you that there is 5% that the project will be delayed, so there is a 95% certainty that the project will be on time within the boundaries provided. 95% of values within the control limits is SIGMA-2 (do some read on 6 sigma to remember Sigma1,2,3 and 6).

Sigma 2 is equal at 2 standard deviations.

So knowing the boundaries of the control limit, which goes from 30 May to 30 June (1 month), and knowing that's equal at 2 standar deviation, you can conclude:

2 Standar deviation = 1 month, so 1 standar deviation = 1/2 month

 

All the other data acts as a distractor. I also got this question wrong the first time :)

Regards,