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CMA Final · Strategic Cost Management · Network Analysis - PERT, CPM

For an activity in a PERT network, the optimistic time is 4 days, the most likely time is 10 days and the pessimistic time is 22 days. What is the expected time of the activity under the beta-distribution approximation?

The expected time is 11 days. PERT weights the most likely estimate four times, so the expected time is (4 + 4×10 + 22)/6 = 11. A simple average of the three estimates would give 12 days, which ignores the beta-distribution weighting.

  1. A10 days
  2. B11 daysCorrect
  3. C12 days
  4. D13 days

Explanation

PERT expected time = (a + 4m + b)/6 = (4 + 40 + 22)/6 = 66/6 = 11 days. The simple average (4 + 10 + 22)/3 = 12 days ignores the weight of 4 on the most likely time, so it is wrong.

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