Question

Consider a PERT network as given below:

The expected activity time is as shown in network above. The probability of completion of above project in 24 days is 95%. Calculate the expected activity time for activity 2 - 3, if standard deviation for project is 2.5.

P(%)	90	94	97
z	1.3	1.5	1.8

• A. 5
• B. 8
• C. 6
• D. 9

Answer 1

The correct option is A 5

For 95% probability, standard variate 'z' can be found by interpolation from table above
For $P=95\%,z=1.5+\frac{0.3}{3}\times 1=1.6$
$\because \frac{T_S-T_E}{\sigma }=z$
$\Rightarrow \frac{24-T_E}{2.5}=1.6$
$\Rightarrow T_E=20$ days
$\Rightarrow 8+x+7=20$
$\Rightarrow x=5$ days