PERT - Standard Deviation doesn't work out on this Question

Submitted by anitkhagram on Sat, 10/04/2014 - 20:10

If you use P-O/6. 3-10/6 = 1.16/ Correct Answer is 11.95.

The standard deviations for the four tasks at the critical path are 3, 5, 10, and 3. What is the standard deviation for the entire critical path?

Choose one answer.
A. You can not determine the standard deviation on critical path. Incorrect
B. 11.95 Correct
C. 5.8 Incorrect
D. 143 Incorrect
Incorrect
Marks for this submission: 0/1.

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saketbansal's picture

saketbansal

Sun, 10/05/2014 - 12:34

In order to calculate the standard deviation of the entire path, you need to sum the variance of entire path and then take sqrt of it

so you have standard deviation given in question , so square of it would be variance
total variance = 3*3 +5*5+10*10+3*3
= 143

Standard Deviation = sqrt (143 ) = 11.95

anitkhagram

Sun, 10/05/2014 - 13:35

Wow thanks. That was pretty cool. I would imagine a lot of people would not get this question correct on the exam. I don't even think the exam calculator has a square root function! lol

Much appreciated sir!
Anit