Standard deviation

Submitted by kiranu23 on Wed, 08/25/2010 - 12:16

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


 


Could anyone solve this and provide explaination please

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pkukilla

Wed, 08/25/2010 - 14:50

 From question you can determine  its 95% probability i.e. 2 Sigma that the project will be delivered before June 30 

ML=May 30

P = Jun 30

May30+2*SD=Jun 30

1 Month = 2SD

SD=1/2 Month

PMzilla_binh

Thu, 11/11/2010 - 08:42

HI pkukilla,

I'm still not clear, from the fomula "May30+2*SD=Jun 30" for normal distribution, it means that probability for project is delivered after 30Jun and before 30Apr is 5% while the provided information is only for after 30Jun

Am I missing something?

Thanks

pkukilla

Thu, 11/11/2010 - 15:40

In the question its written 5% probability that it will exceed June 30th ie. 95% probability that it wont exceeded June 30th.

May 30th= ML 

June30th = Pesemic

 

May 30th+ 4 weeks = June 30th -->(1)

May 30th +2 * SD = June 30th --> (2)

(1)-(2)--> 2SD = 4 weeks

1 SD= 2 weeks.  or 1/2 month.

 

 

 

PMzilla_binh

Mon, 11/22/2010 - 10:10

Hi pkukilla,

If you're rightI guess i have a big hole in my knowledge, it's good chance to fill-in, so pls be patient with me.

Some query:

1. Though the question does not state this probability base on normal distribution. Are we assuming this? (Yes, right)

2. If it's normal distribution, the probability that schedule in [ML -2*sigma, ML+ 2* sigma] would be 95% and the probability that schedule out of [ML+2*sigma] is only 2.5%

Mapping to this question, the probability that it's over 30 Jun will be only 2.5%.

Kindly help to point out where is the hole in my explanation. Thanks!

pkukilla

Mon, 11/22/2010 - 16:11

 There is nothing assumed. Please re-read the qn