How was the answer gotten!

Submitted by Latunde on Wed, 05/14/2014 - 06:56
You are responsible for Quality Audit in an Ongoing Project. The Audit has an optimistic estimate of ten days, pessimistic estimate of sixteen days, and most likely estimate of thirteen days. Assuming a normal distribution, what is the probability that the Audit will be completed within 10 to 16 days?
 
 
  Choice 1 99.99 %
 
  Choice 2 99.73 %
 
  Choice 3 95.46 %
 
  Choice 4 68.26%
 
 
  Correct Choice : 2
 
got the answer correctly but used residual knowledge but want to know how the answer was derived.
 
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sunku65

Wed, 05/14/2014 - 10:12

Step 1 : Calculate Duration.  = (O + 3M + P)/6  = (10 + 4x13 + 16)/6  = 78/6  = 13 days

Step 2 : Calculate Standard Diviation  = P - O/6 = (16 - 10)/6  = 6/6  = 1 day

1 Sigma =68.26% = 1SD =  1x1  = 1 day

2 sigma = 95.46% = 2 SD =  2x1 = 2 days

3 sigma = 99.73% = 3 SD =  3 x 1= 3 days

6 sigma = 99.99% = 6 SD  = 6 x1  =6 days.

Therefore the  % of the pobability that the audit will be completed =  Duration +/- SD

6 Sigma =99.99% of probability that the Audit will be completed within = 13 +/-6  = 7 to 19 days.

3 Sigma =99.73% of probability that the Audit will be completed within = 13 +/-3  = 10 to 16 days.

2 Sigma =95.46% of probability that the Audit will be completed within = 13 +/-2  = 11 to 15 days.

1 Sigma =96.26% of probability that the Audit will be completed within = 13 +/-1  = 12 to 14 days.

Now you can compare which values suitable to the asking range i.e. 10 to 16 days.

The answer is 3 sigma standard, 99.73% probability audit will be completed within 10 to 16 days.

 

farhanmazhari

Wed, 05/14/2014 - 11:10

Can we expect similar type of question in exam?

sunku65

Wed, 05/14/2014 - 13:13

May be.  But, the writ-up content of the quastion may be very lenthy.  

Sundara.damaraj...

Wed, 05/14/2014 - 13:21

kumarks984

Wed, 05/14/2014 - 13:31

Hey thank you for the detailed write up but a quick question...I was confused on to when to decide to use triangular distribution & when to use beta distribution, as I started doing the calculation using (P+R+O/3), could you assist me with the differentiation?

 

 

sunku65

Wed, 05/14/2014 - 15:31

I thought normal distribution is a traditional Pert Distribution,  i.e (O+4m+P)/6.

In PMBOK5 named Beta Distribution.(Electonic version of PMBOK Page 171) is also samething.

Whereas you mentioned is a Triangular Distrubution i.e. newly introduced in PMBOK5.

I think this question from Old Version.

 

sunku65

Wed, 05/14/2014 - 15:35

Bye the bye in this question the duration of BETA Distribution and Triangular Distribution is equal to 13.

kumarks984

Wed, 05/14/2014 - 20:05

That's true either way it's 13....but technique wise normally it is BETA distribution....cool...thank you...

Latunde

Wed, 05/14/2014 - 21:02

Is the original all but is the Original formular beta or normal distribution?

Thanks