How to calculate the Probability distiribution
Submitted by kmkan28 on Thu, 02/28/2013 - 14:25
Hi,
I have got this below question from one of the mock test.I am not able to get the calculation.
Given that completion time of a particular project has an expected value of 8 weeks and a standard deviation of two weeks ,and assuming that completion time is normally distributed,what is the probability of completing the project within 10 weeks
A.0.5
B.0.84
C.0.95
D.0.997
Please let me know the explanation
Forums:
sspawar
Thu, 02/28/2013 - 15:07
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It is good question, and I
It is good question, and I think - it is little different , than so far asked.
There are mainly four pobability distibution curve - mentioned in PMBOK also.
question is saying - normally distributed -- means normal distribution curve
It is same like we say for
+/- 1 sigma = 68.26 % area means 0.6826 proability, in figure if you will see left side of the mean (middle pick) is half of this 68.26 - 34.13%, and right side of the mean is also half of this 68.26 = 34.13%. lfet side called - (minus ) one sigma , right side called +(plus) one sigma.
like
+/-2 sigma = 95.46 % area means 0.9546 probability
-------------------------------------------------------------------------------
now come to the question
sigma = 2 weeks
10 weeks means 8+2 week = mean + right side one sigma
corrosponding area
Left side complete area of curve up to mean ,is half of full bell shape curve = 50%
Right side 1 sigma area = 34.13%
=> 50+34.13 = 84.13, hence total probability is 0.8413, Answer is B
refer both figures of following thread:
http://er-sspawar.blogspot.in/2012_05_29_archive.html
kmkan28
Thu, 02/28/2013 - 16:22
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It is awesome
Pawar,
Thanks for your reply with the explanation.Indeed i was not aware of this much details and since you come from Civil engineering experience it helped me a lot.I am continuously attending the mock test and now i am able to answer on quetions with the similar format.
I have one more question likely the same which will be posted after some time.
Thanks,
Mani
sspawar
Fri, 03/01/2013 - 01:32
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You are right. Definitely
You are right.
Definitely it is easy to learn maths part for an Engineer.
What is your next question.
sunitaPMP
Fri, 03/01/2013 - 07:41
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do we get such type of
do we get such type of questions in real exam?
kmkan28
Fri, 03/01/2013 - 10:10
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This is also my question
Do we get such type of questions in the PMP exam.Definately it will cosume time for non-maths proficients and other non subject matter experts?
Mani
sspawar
Fri, 03/01/2013 - 11:33
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I believe this is not a
I believe this is not a lengthy or time taking question.
If your concepts are good then it is a half minute question
See given, SD =2, Mean = 8 , where will stay 10.
it is very easy now when you have been understood the concept.
50 (mean) +34(one sigma rt side)
kmkan28
Fri, 03/01/2013 - 11:44
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Pawar,Yes,understanding the
Pawar,
Yes,understanding the question is key point.I understood after you have given the explanation for this question.
Likely if you have any such questions in other probablity distribution (ex: beta..etc.) please share in this forum.
Mani
sspawar
Fri, 03/01/2013 - 17:30
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here are 2
here are 2 questions
http://er-sspawar.blogspot.in/2012/12/15-chance-you-will-exceed-estimate...
http://er-sspawar.blogspot.in/2012_05_29_archive.html
sunitaPMP
Fri, 03/01/2013 - 19:16
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Honestly am not clear about
Honestly am not clear about this concept.Can you tell em where can I check this?Any link?I do not understand why this bell shpe,what is 50 % etc...Can you pls send me soem link to get thos eidea?
I just know how to calculate SD but i can not map this to that bell shaped curve.
Tahnks in advance...
sunitaPMP
Fri, 03/01/2013 - 19:17
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Hello Pawar jiHonestly am not
Hello Pawar ji
Honestly am not clear about this concept.Can you tell em where can I check this?Any link?I do not understand why this bell shpe,what is 50 % etc...Can you pls send me soem link to get thos eidea?
I just know how to calculate SD but i can not map this to that bell shaped curve.
Tahnks in advance...
sspawar
Sat, 03/02/2013 - 01:23
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you can refer youtubes on
you can refer youtubes on normal distribution curve and web sites mathisfun, wolform etc
for 50% remember NMD curve have mean value (mue) in middle , and either side of it have equal space 50-50 below curve based on x axis.
remember
6sigma = 99.99966/2 = 49.99999% not 50%
it is infinite curve.
sspawar
Sun, 03/03/2013 - 13:50
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Sunita ji you want to know how
Sunita ji
you want to know how bell shape curve formed?
I try my best to explain this:
for example you are checking1000 tests given by pmp aspirants.
your standard value of profeciency is suppose 150 out of 200
this standard value 150 will be called as MEAN value.
now you observe that --- some students are performing better than this , some are below this.
then you make a table of marks at X axis against frequency of students obtaining that marks at Y axis
Values = Marks at X axis
Frequency =Nos of students at Y axis
100
30
110
45
120
100
130
120
140
135
150
150
160
130
170
125
180
90
190
45
200
30
Total
1000
sspawar
Sun, 03/03/2013 - 13:51
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If it comes in following
If it comes in following shape --- it will be called as normally distributed.
µ
MEAN