You are working on calculating the estimation for a project. You have been given the following numbers by your manager, who is considered to be an expert in estimation: Optimistic = 35 days Likely =…

Question

Options

• AE is 46.3 days, SD = 35
• BE is 40 days, SD = 6.67
• CE is 37.3 days, SD = 43.3
• DE is 43.3 days, SD = 5

• A
  10% (3)
• B
  17% (5)
• C
  3% (1)
• D
  69% (20)

Explanation

Option D is correct because it correctly applies the PERT three-point estimation formulas:

• E = (O + 4M + P) / 6 = (35 + 4×40 + 65) / 6 = 260 / 6 = 43.3 days
• SD = (P − O) / 6 = (65 − 35) / 6 = 5

Why the distractors are wrong:

• A (E=46.3, SD=35) - Both values are wrong; SD=35 is just the Optimistic value, not a deviation calculation.
• B (E=40, SD=6.67) - E=40 is simply the Most Likely value with no weighting applied; SD=6.67 doesn't follow the correct formula either (looks like 40/6).
• C (E=37.3, SD=43.3) - Both values are nonsensical; the SD cannot be larger than the range of estimates, and E is lower than the Optimistic value.

Memory tip: Remember the formula as "the 4 goes to the middle" - 4× the Most Likely value is the key weight because it represents the most probable outcome. For SD, think "Pessimistic minus Optimistic, divided by 6" - it measures how spread out (uncertain) your estimate is.

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