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GATE 2021 ME (ME2) – Question 18

Operations Research · Network flow models, PERT and CPM · 1 mark · Multiple choice

A PERT network has 9 activities on its critical path. The standard deviation of each activity on the critical path is 3. The standard deviation of the critical path is

  1. 3
  2. 9
  3. 27
  4. 81

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Show answer and explanation

Correct answer: (B) 9

Explanation

Independent activity variances add. Each variance is 3²=9, so total path variance is 9×9=81.

Take the square root to obtain **standard deviation 9 (B)**. Adding standard deviations directly would incorrectly give 27.