| Exam Board | Edexcel |
|---|---|
| Module | D1 (Decision Mathematics 1) |
| Year | 2013 |
| Session | June |
| 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 critical path analysis question requiring students to draw an activity network with dummy activities and explain their necessity. While it requires understanding of precedence relationships and the specific purpose of dummies (avoiding duplicate arcs and representing dependencies), it's a routine textbook exercise with well-established rules. The two-dummy constraint guides students to the correct solution, making it slightly easier than average A-level questions. |
| Spec | 7.05a Critical path analysis: activity on arc networks |
| 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 |
**Question 6 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
- 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)6.
\begin{center}
\begin{tabular}{|l|l|}
\hline
Activity & Immediately preceding activities \\
\hline
A & - \\
\hline
B & - \\
\hline
C & A \\
\hline
D & A \\
\hline
E & B \\
\hline
F & C D \\
\hline
G & D \\
\hline
H & F G \\
\hline
I & H \\
\hline
J & H \\
\hline
K & I J \\
\hline
\end{tabular}
\end{center}
\begin{enumerate}[label=(\alph*)]
\item Draw the activity network described in the precedence table, using activity on arc and exactly two dummies.\\
(5)
\item Explain why each of the two dummies is necessary.\\
(2)
\end{enumerate}
\hfill \mbox{\textit{Edexcel D1 2013 Q6 [7]}}