# Probability - Anyone can explain? how was the answer derived?

Question: You are responsible for Quality Audit in an Ongoing Project. The Audit has an optimistic estimate of ten days, pessimistic estimate of sixteen days, and most likely estimate of thirteen days. Assuming a normal distribution, what is the probability that the Audit will be completed within 10 to 16 days?

Answer: In a normal distribution, the

PERT duration (also called mean) {Pessimistic + (4* Most Likely) + Optimistic} / 6 = {16 + (4 * 13) + 10}/6 = 13 days

1 Standard Deviation (sigma) = (Pessimistic - Optimistic) / 6 = (16 - 10) / 6 = 1 day

If the task has to be completed within 10 days to 16 days, then the probability of completion within the time frame is __ 99.73%__ (3 sigma) as shown in the Six Sigma exhibit.

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Fri, 02/07/2014 - 03:32

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## Since it assumes normal

Since it assumes normal distribution, you take 3sigma deviation