D1 June 2013 (R) Q6
6.
| Activity | Immediately preceding activities |
|---|---|
| A | – |
| B | – |
| C | A |
| D | A |
| E | B |
| F | C D |
| G | D |
| H | F G |
| I | H |
| J | H |
| K | I J |
(a) Draw the activity network described in the precedence table, using activity on arc and exactly two dummies. (5)
(b) Explain why each of the two dummies is necessary. (2)
| Scheme | Marks |
|---|---|
 | M1 A1 (One start A – E) A1 (F – J + dummy 1) A1 (K + dummy 2) A1 (all arrows + finish) |
| (5) |
Notes
a1M1 7 activities and one dummy placed. Must be considering activity on arc (activity on node is M0).
a1A1 One start + A, B, C, D and E dealt with correctly.
a2A1 F, G, H, I and J and 1st dummy dealt with correctly.
a3A1 K and 2nd dummy dealt with correctly.
a4A1 CSO - all arrows present and correctly placed with one finish.
| Scheme | Marks |
|---|---|
| 1st dummy – G depends on D only, F depends on C and D. | B1 |
| 2nd dummy – I and J must be expressed uniquely in terms of their end events. | B1 |
| (2) | |
| (7 marks) |
Notes
b1B1 First dummy correctly described (C, D, F and G referred to)
b2B1 Second dummy correctly described (mention of ‘uniqueness’ alone is not sufficient for this mark).