Question on Mean

Submitted by mpavas on Tue, 12/11/2012 - 15:35

This is a question from rita fast track.

You just completed a cost estimate on the project, and you are assuming that there is a 15% chance you will exceed this estimate. You are:

a Below the mean

b. Above the mean

c. Above the median

d. Belotthe median

Please let me know the rational behind the answer and how can i understand more about this question.

 

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aarush78

Wed, 12/12/2012 - 04:32

Is this a complete question ..there is no information related to the current mean/SD or basis of estimate like was it +- 3sigma or how was it calculated


Are you sure there is nothing else in the information and is a complete one


 

sspawar

Wed, 12/12/2012 - 09:09

Perhaps, It has a definite answer with this information.

B above the mean

Question is saying - there is 15% chance that you will exceed this estimate, means your estimate is at 85% value and Mean means 50% area (middle)of bell curve (normal dist curve). (sometimes beta dist curve - incase of 3point pert estimation)

Please refer my blogspot   http://er-sspawar.blogspot.in/

1.645 HAVE 45% AREA FROM MEANTHREE POINT ESTIMATE AND SD 
NORMAL DISTRIBUTION CURVE
 
one thing more - reeta software has explanation slide for every question. what is written there, PAVAS may elaborate that here.

Regards

mpavas

Wed, 12/12/2012 - 17:33

 Let me try to find that answer give me some time will post it in few hrs

mpavas

Wed, 12/12/2012 - 17:34

 Let me try to find that answer give me some time will post it in few hrs

aarush78

Thu, 12/13/2012 - 03:17

Dear SSpawar


While we wait for the question creator's solution from rita i have a doubt when you say "there is 15% chance that you will exceed this estimate, means your estimate is at 85% value " ..i agree with the meaning or your interpretation of this standalone statement


But lets take some hypothetical figures and say mean is 100$ ..Now the question does not say anything about "relative positioning of the given estimate w.r.t mean" ..the estimate could be lets say $50 and only inference drawn is that 85% probability is there that actual cost will come somewhere around $50 and 15% chances are that it will exceed $50


Thats why i thought there are some more inputs either missing in the question itself or we have to make some serious assumption


I know if i had to answer the question while taking an intelligent guess i would choose Above mean but since in this forum we have option to disucss the reasoning i thought lets establish the logic how do you relate any given "independent" estimate with reagrd to mean when nothing about is given in question

sspawar

Thu, 12/13/2012 - 05:55

Dear Puneet

I think values are not needed.

Your main query is - "relative positioning of the given estimate w.r.t mean"

Here is the justification:

If we observe figure 11.16 minutely -- you may see that Mean Estimate Value means => Value at 50%Probability.

Now there is already an example,

as per PMBOK example its value on this statistical - curve is observed only 12 % probability (chance) that estimate will meet the event.

Like this Rita is asking ---- you are already clear about this. 

So with such type of questions -- this is universal concept that chances of 50% meeting the value in the event means it is mean value of any statistical simulations, like Normal distribution curve or pert beta distribution curve.

In other way PERCENT means = out of 100. Fifty is mean . 85 is above 50.

Regards

sspawar

Wed, 12/12/2012 - 12:27

This question can also be understood by figure 11.16 of PMBOK P 300. 

Here

Don't confuse that curve is not bell curve but it is cumulative disribution function curve. It always remain in S shape.

While Bell curve (normal dis curve or beta dis curve ) remains closed like inverse U.

sspawar

Fri, 12/14/2012 - 10:27

RITA Q ID 620 and her explanation

The correct answer is B.

With normal distribution, the mean indicates you have a 50 perent chance of being over or under your estimate. Since you have only a 15 percent chance of being over, you are above (or to the right of) the mean. 

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