Moderate -0.8 Part (a) requires drawing a standard activity network with dummies, a routine D1 skill tested frequently. Part (b) asks for textbook explanation of why dummies exist (to show precedence/avoid duplicate arcs). This is straightforward recall and application with no problem-solving or novel insight required.
Draw the activity network described in the precedence table, using activity on arc. Your activity network must contain only the minimum number of dummies.
(5)
Explain why, in general, dummies may be required in an activity network.
Network diagram with 8 activities (labelled on arc), one start and at least one dummy placed
M1
Activities A, B, 1st dummy (+ arrow) and C, D and E dealt with correctly.
A1
2nd dummy (+ arrow) and F, G and K dealt with correctly.
A1
Activities H, I, 3rd dummy (+ arrow) and J dealt with correctly.
A1
CSO – all arrows present and correctly placed with one finish.
A1 (5)
Dummies are needed to show either – dependency where subsequent activities do not all depend on the same preceding activities – that an activity can be uniquely represented in terms of its end events
B1 B1 (2)
7 marks
Notes for Question 5:
In (a) condone lack of, or incorrect, numbered events throughout – also 'dealt with correctly' means that the activity starts from the correct event but may not finish at the correct event. Activity on node is M0.
Do not penalise the same error twice with the first three A marks, for example, if activity C is not labelled (but the arc is present) then this will lose the first A mark and the final (CSO) A mark – they can still earn the second and third A marks.
- a1M1: Eight activities (labelled on arc), one start and at least one dummy placed.
- a1A1: Activities A, B, 1st dummy (+ arrow) and C, D and E dealt with correctly.
- a2A1: 2nd dummy (+ arrow) and F, G and K dealt with correctly.
- a3A1: Activities H, I, 3rd dummy (+ arrow) and J dealt with correctly.
- a4A1: CSO – all arrows present and correctly placed with one finish.
Penalise lack of, or incorrect, arrows on the dummies only once with the first three A marks (on the first occurrence).
- b1B1: Dependency + some explanation of what this means, bod – allow a correct example using any nodes/letters.
- b2B1: Uniqueness – please note that, for example, 'so that activities can be defined uniquely' is not sufficient to earn this mark. There must be some mention of describing activities either in terms of the event at each end or in terms of an activities events. However, give bod on statements that imply that an activity begins and ends at the same event.
| Answer | Marks | Guidance |
|--------|-------|----------|
| Network diagram with 8 activities (labelled on arc), one start and at least one dummy placed | M1 | |
| Activities A, B, 1st dummy (+ arrow) and C, D and E dealt with correctly. | A1 | |
| 2nd dummy (+ arrow) and F, G and K dealt with correctly. | A1 | |
| Activities H, I, 3rd dummy (+ arrow) and J dealt with correctly. | A1 | |
| CSO – all arrows present and correctly placed with one finish. | A1 (5) | |
| Dummies are needed to show either – dependency where subsequent activities do not all depend on the same preceding activities – that an activity can be uniquely represented in terms of its end events | B1 B1 (2) | |
| | 7 marks | |
**Notes for Question 5:**
In (a) condone lack of, or incorrect, numbered events throughout – also 'dealt with correctly' means that the activity starts from the correct event but may not finish at the correct event. **Activity on node is M0.**
Do not penalise the same error twice with the first three A marks, for example, if activity C is not labelled (but the arc is present) then this will lose the first A mark and the final (CSO) A mark – they can still earn the second and third A marks.
- a1M1: Eight activities (labelled on arc), one start and at least one dummy placed.
- a1A1: Activities A, B, 1st dummy (+ arrow) and C, D and E dealt with correctly.
- a2A1: 2nd dummy (+ arrow) and F, G and K dealt with correctly.
- a3A1: Activities H, I, 3rd dummy (+ arrow) and J dealt with correctly.
- a4A1: CSO – all arrows present and correctly placed with one finish.
**Penalise lack of, or incorrect, arrows on the dummies only once with the first three A marks (on the first occurrence).**
- b1B1: Dependency + some explanation of what this means, bod – allow a correct example using any nodes/letters.
- b2B1: Uniqueness – please note that, for example, 'so that activities can be defined uniquely' is not sufficient to earn this mark. There must be some mention of describing activities either in terms of the event **at each end** or in terms of an activities events. However, give bod on statements that imply that an activity begins and ends at the same event.
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5.
\begin{center}
\begin{tabular}{ | c | c | }
\hline
Activity & Immediately preceding activities \\
\hline
A & - \\
\hline
B & - \\
\hline
C & A \\
\hline
D & A \\
\hline
E & A, B \\
\hline
F & C \\
\hline
G & C, D \\
\hline
H & E \\
\hline
I & E \\
\hline
J & H, I \\
\hline
K & F, G \\
\hline
\end{tabular}
\end{center}
\begin{enumerate}[label=(\alph*)]
\item Draw the activity network described in the precedence table, using activity on arc. Your activity network must contain only the minimum number of dummies.\\
(5)
\item Explain why, in general, dummies may be required in an activity network.
\end{enumerate}
\hfill \mbox{\textit{Edexcel D1 2015 Q5 [7]}}