Week 2 - Tutorial Questions Network Anlaysis

Question 1

How do you calculate the Probability of a project taking less than ‘X’ weeks/days?

Answer 1

1) Calculate the mean of the project (using network diagram).
2) Calculate the variance of each activity in the critical path. ((Tp-To)/S)2)
3) Sum the variance of the critical path and square root the answer to find the standard deviation.
4) Find the Z-score to look up (Z=(x-m)/s)
5) Look up Z-score on table and convert into a percentage probability.

Question 2

How do you calculate the probability that a project finished between ‘X” and ‘X1’?

Answer 2

1) Calculate the standard deviation of the project (By calculating the variance of each activity in the critical path and square rooting the answer).
2) (X-M)/S for both of the range values.
3) Find the closest number to the values found in step 2 on the z-table and take note of what they correspond to.
4) We now know the probability of the project being outside of X and X1.
4) Calculate 1 Less the probability of the project being outside of the range. (This leaves the Probability that the project will be within this range)

Question 3

There is a 90% chance the project will take X weeks to complete, what is the value of X in weeks.

How is this sort of question calculated?

Answer 3

1) Find the missing value from part 1 of the question, in this case it is 10% 0r 0.10.
2) Look up 0.10 on the Z-table and find the closest value and its corresponding Z-score.
3) Use the formula: Mean + Z-score x Standard deviation

Question 4

What does the dotted line on a gantt chart represent?

Answer 4

The total float of the activity

Question 5

What does the solid line on a gantt chart represent?

Answer 5

Represent the length of the activity

Question 6

If we want to reduce the chance of the project taking longer than 20 weeks to 1%, How much do we need to reduce average time?

Answer 6

1) What value is missing? 1% or 0.01
2) What is the closest value to this in the z-table? (0.00990)
3) What does 0.00990 correspond to in Z-table? (2.33)
4) Mean + Z-score x Standard deviation = 16.16 days

Question 7

What is one limitation of PERT analysis?

Answer 7

The variation of activities outside of the critical path are ignored.

Some may have high variance and therefore a chance of impacting upon the project.