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TOPIC: Doubt in Standard deviation ...

Doubt in Standard deviation ... 7 years 1 month ago #1365

  • Karthikeyan Subramanian
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I came thru the below 2 questions. I am confused after checking the answers given for the question.

Question 1 :
Using the information below and assuming the critical path consists of three consecutive tasks A, B, and C, the probability of completing this project within 13 days is
Activity Optimistic Estimate Most Likely Estimate Pessimistic Estimate
A 2 3 4
B 4 4.5 8
C 2 4 6

a. 50%
b. 68%
c. 84%
d. 95%
My answer is 68% as 13 days +1SD from 12 days. My assumption is 68.26 cna be considered as 68 as round off
Answer given is 85%.

Question 2 The cost estimate of a proposed project has an expected value of $1,000,000 and a standard deviation of $50,000. The project is budgeted for $1,100,000 so as to include a contingency reserve. Assuming that cost estimates are normally distributed, what is the probability of completing this project over budget?
a. 10%
b. 5%
c. 2.5%
d. 50%

My answer : 5% as the SD is +2SD and for over budget there are changes of the rest 5%. My asusmption is 95.46 can be considered as 95 as round off.

Please help
Given answer is 2.5%

Re:Doubt in Standard deviation ... 7 years 3 weeks ago #1376

  • Orkun Toros
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Karthikeyan,

Both of your answers are correct according to my calculations.

-The first question is definitely 12+1SD
-The second question is $100,000+2SD and since it is a normal distribution, the confidence level is 95%.
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