| Exam Board | Edexcel |
|---|---|
| Module | D1 (Decision Mathematics 1) |
| Year | 2008 |
| Session | January |
| Marks | 7 |
| Paper | Download PDF ↗ |
| Mark scheme | Download PDF ↗ |
| Topic | Critical Path Analysis |
| Type | Explain dummy activities |
| Difficulty | Moderate -0.3 This is a standard D1 activity network question requiring routine application of dummy activity rules. Part (a) involves drawing a network following given precedence constraints—a mechanical task once the technique is learned. Part (b) tests understanding of why dummies are needed (to show correct precedence and avoid duplicate activities), which is textbook knowledge requiring minimal problem-solving. Slightly easier than average as it's a direct application of a well-practiced algorithm with no novel reasoning required. |
| Spec | 7.05a Critical path analysis: activity on arc networks |
| Activity | Immediately preceding activities |
| A | - |
| B | - |
| C | A |
| D | B |
| E | B, C |
| F | B, C |
| Answer | Marks | Guidance |
|---|---|---|
| Answer | Marks | Guidance |
| Activity on arc, all activities present | M1 | Condone lack of events |
| \(A, B, C, D\) and first dummy correct | A1 | |
| \(E, F\) and second dummy correct (on \(E\) or \(F\)) | A1 | |
| All arrows including on dummies, one start and one finish | A1 |
| Answer | Marks | Guidance |
|---|---|---|
| Answer | Marks | Guidance |
| Dummy 1 is needed to show dependancy: \(E\) and \(F\) depend on \(C\) and \(B\), but \(D\) depends on \(B\) only | B1 | Dummy 1 correctly justified – give bod |
| Dummy 2 is needed so that each activity can be uniquely represented in terms of its events | B1 | Dummy 2 correctly justified – give bod |
| B1 | A bonus for two good answers |
# Question 5:
## Part (a):
| Answer | Marks | Guidance |
|--------|-------|----------|
| Activity on arc, all activities present | M1 | Condone lack of events |
| $A, B, C, D$ and first dummy correct | A1 | |
| $E, F$ and second dummy correct (on $E$ or $F$) | A1 | |
| All arrows including on dummies, one start and one finish | A1 | |
## Part (b):
| Answer | Marks | Guidance |
|--------|-------|----------|
| Dummy 1 is needed to show dependancy: $E$ and $F$ depend on $C$ and $B$, but $D$ depends on $B$ only | B1 | Dummy 1 correctly justified – give bod |
| Dummy 2 is needed so that each activity can be uniquely represented in terms of its events | B1 | Dummy 2 correctly justified – give bod |
| | B1 | A bonus for two good answers |
---5. (a) Draw the activity network described in this precedence table, using activity on arc and exactly two dummies.\\
(4)
\begin{center}
\begin{tabular}{|l|l|}
\hline
Activity & Immediately preceding activities \\
\hline
A & - \\
\hline
B & - \\
\hline
C & A \\
\hline
D & B \\
\hline
E & B, C \\
\hline
F & B, C \\
\hline
\end{tabular}
\end{center}
(b) Explain why each of the two dummies is necessary.\\
(3)\\
\hfill \mbox{\textit{Edexcel D1 2008 Q5 [7]}}