D1 January 2008 Q5
5.
(a) Draw the activity network described in this precedence table, using activity on arc and exactly two dummies. (4)
| Activity | Immediately preceding activities |
|---|---|
| \(A\) | - |
| \(B\) | - |
| \(C\) | \(A\) |
| \(D\) | \(B\) |
| \(E\) | \(B\), \(C\) |
| \(F\) | \(B\), \(C\) |
(b) Explain why each of the two dummies is necessary. (3)
| Scheme | Marks |
|---|---|
E.g. | M1 A1 A1 A1 |
| (4) |
Notes
Q5(a) 1M1 Activity on arc, all activities present, condone lack of events
1A1 A,B,C,D and first dummy correct
2A1 E, F and second dummy correct (on E or F)
3A1 All arrows – including on dummies, one start and one finish
| Scheme | Marks |
|---|---|
| Dummy 1 is needed to show dependancy. E and F depend on C and B, but D depends on B only | |
| Dummy 2 is needed so that each activity can be uniquely represented in terms of its events. | B3, 2, 1, 0 |
| (3) | |
| (7 marks) |
Notes
(b) 1B1 Dummy 1 correctly justified – give bod
2B1 Dummy 2 correctly justified – give bod
3B1 A bonus for two good answers