A PERT network has three activities on critical path with mean time 3, 8 and 6 and standard deviations 1, 2 and 2 respectively. The probability that the project will be completed in 20 days is

A. 0.50

B. 0.66

C. 0.84

D. 0.95

Answer: Option C

Solution(By Examveda Team)

Standard deviation = square root of (variance) = square root of (1 * 1 + 2 * 2 + 2 * 2) = square root of (9) = 3
D = 20
S = 3 + 8 + 6 = 17
Probability $$ = \frac{{\left( {{\text{D}} - {\text{S}}} \right)}}{{{\text{standard deviation}}}} = 1$$
Now, from Z table probability = 0.84.