Due to an influx of spam in our forums we have disabled posting for guests. Guests can still read the forum, but you have to login in order to start or participate in a discussion.
Welcome, Guest
NEVER post copyrighted questions. Always state where questions come from. We take copyright violations very serious. Any copyrighted materials will be removed and the posters account will be deactivated.

TOPIC: Why is this the correct answer?

Why is this the correct answer? 2 years 5 months ago #4588

  • Offline
  • Fresh Boarder
  • Posts: 4
  • Thank you received: 1
  • Karma: 0

I don't understand how this answer was calculated for the question from Oliver Lehmann's free 75 question test.
Can anyone please enlighten? The correct answer is B ie. approx. 5.2 days.

27. A project manager made 3-point estimates on a critical path and found the following results: (Check attached table below)

Assuming ±3 sigma precision level for each estimate, what is the standard deviation of the allover path?

(A) App. 4.2 days
(B) App. 5.2 days
(C) App. 6.2 days
(D) You can not derive the path standard deviation from the information given.

The administrator has disabled public write access.

Why is this the correct answer? 2 years 1 month ago #4985

  • Nicholas Croglio
  • Nicholas Croglio's Avatar
  • Offline
  • Fresh Boarder
  • Posts: 5
  • Karma: 0
I am sure you have long since figured this out, but for those that have this question like I did. I have included one possible solution after playing around.

Variances are additive, and standard deviation is the square root of variance.

We can calculate the std of each activity, by subtracting the optimistic from the pessimistic.

That yields


Then add up the squares of the std deviations to get the total variance.

Total Variance = 27

Then take the square root to get 5.2
The administrator has disabled public write access.
Moderators: Yolanda Mabutas, Ahmed Amin, Scott Gillard, Fernando Jr Sinlao Lim, Mary Kathrine Padua, Chris Preziotti, Lazard Toe, ITBMC, MPM, CIPM, PMP, ITIL, Christian Winter, Kevin Nason, Mark Wuenscher, PMP

Training for Project Management Professional (PMP)®, PMI Agile Certified Practitioner (PMI-ACP)®, and Certified Associate in Project Management (CAPM)®