| Exam Board | AQA |
|---|---|
| Module | D2 (Decision Mathematics 2) |
| Year | 2007 |
| Session | January |
| Marks | 13 |
| Paper | Download PDF ↗ |
| Mark scheme | Download PDF ↗ |
| Topic | Matchings and Allocation |
| Type | Hungarian algorithm for maximisation |
| Difficulty | Moderate -0.5 This is a standard application of the Hungarian algorithm with straightforward table manipulation. Part (a) requires simple recall that the algorithm minimises (so maximisation requires transformation), part (b) is mechanical execution of a well-defined algorithm taught in D2, and part (c) involves a minor constraint modification. The algorithm itself is procedural rather than requiring mathematical insight, making this easier than average A-level questions that demand problem-solving or proof. |
| Spec | 7.04a Shortest path: Dijkstra's algorithm |
| Job 1 | Job 2 | Job 3 | Job 4 | Job 5 | |
| Alex | 13 | 11 | 9 | 10 | 13 |
| Bill | 15 | 12 | 12 | 11 | 12 |
| Cath | 12 | 10 | 8 | 14 | 14 |
| Don | 11 | 12 | 13 | 14 | 10 |
| Ed | 12 | 14 | 14 | 13 | 14 |
| Answer | Marks | Guidance |
|---|---|---|
| Answer | Marks | Guidance |
| Hungarian algorithm minimises | E1 | |
| \(15 - x\) gives measure of criteria NOT met, which need minimising in order to maximise scores | E1 | Idea of high becoming low, etc. Total: 2 |
| Answer | Marks | Guidance |
|---|---|---|
| Answer | Marks | Guidance |
| Array giving \(15 - x\): \(\begin{pmatrix}2&4&6&5&2\\0&3&3&4&3\\3&5&7&1&1\\4&3&2&1&5\\3&1&1&2&1\end{pmatrix}\) | B1 | |
| Reduce rows (or columns then rows): \(\begin{pmatrix}0&2&4&3&0\\0&3&3&4&3\\2&4&6&0&0\\3&2&1&0&4\\2&0&0&1&0\end{pmatrix}\) | M1 | Reduce rows (or columns then rows) |
| Reduced array correct | A1 | |
| Zeros can be covered with only 4 lines, so adjustment needed | E1 | Augmented array shown |
| Reduction by subtracting 1 from each uncovered element | M1 | |
| And adding 1 to each element at intersection of two lines | A1 | |
| Matching on particular zeros | M1 | |
| \(\text{Alex} \leftrightarrow 5\), \(\text{Don} \leftrightarrow 3\), \(\text{Bill} \leftrightarrow 1\), \(\text{Ed} \leftrightarrow 2\), \(\text{Cath} \leftrightarrow 4\) | A1 | If adjustment not done correctly and matching made, award B1 for 3 correct and B1 for rest correct. Total: 8 |
| Answer | Marks | Guidance |
|---|---|---|
| Answer | Marks | Guidance |
| Deleting row 2 and column 4 either in final matrix or reworking | M1 | |
| Final solution: \(A \leftrightarrow 1\), \(C \leftrightarrow 5\) | A1 | |
| \(D \leftrightarrow 3\), \(E \leftrightarrow 2\) | A1 | If no method award B2 if matching is all correct. Total: 3 |
# Question 2:
## Part (a)
| Answer | Marks | Guidance |
|--------|-------|----------|
| Hungarian algorithm **minimises** | E1 | |
| $15 - x$ gives measure of criteria NOT met, which need minimising in order to maximise scores | E1 | Idea of high becoming low, etc. **Total: 2** |
## Part (b)
| Answer | Marks | Guidance |
|--------|-------|----------|
| Array giving $15 - x$: $\begin{pmatrix}2&4&6&5&2\\0&3&3&4&3\\3&5&7&1&1\\4&3&2&1&5\\3&1&1&2&1\end{pmatrix}$ | B1 | |
| Reduce rows (or columns then rows): $\begin{pmatrix}0&2&4&3&0\\0&3&3&4&3\\2&4&6&0&0\\3&2&1&0&4\\2&0&0&1&0\end{pmatrix}$ | M1 | Reduce rows (or columns then rows) |
| Reduced array correct | A1 | |
| Zeros can be covered with only **4 lines**, so adjustment needed | E1 | Augmented array shown |
| Reduction by subtracting 1 from each uncovered element | M1 | |
| And adding 1 to each element at intersection of two lines | A1 | |
| Matching on particular zeros | M1 | |
| $\text{Alex} \leftrightarrow 5$, $\text{Don} \leftrightarrow 3$, $\text{Bill} \leftrightarrow 1$, $\text{Ed} \leftrightarrow 2$, $\text{Cath} \leftrightarrow 4$ | A1 | If adjustment not done correctly and matching made, award B1 for 3 correct and B1 for rest correct. **Total: 8** |
## Part (c)
| Answer | Marks | Guidance |
|--------|-------|----------|
| Deleting row 2 and column 4 either in final matrix or reworking | M1 | |
| Final solution: $A \leftrightarrow 1$, $C \leftrightarrow 5$ | A1 | |
| $D \leftrightarrow 3$, $E \leftrightarrow 2$ | A1 | If no method award B2 if matching is all correct. **Total: 3** |
---
2 Five successful applicants received the following scores when matched against suitability criteria for five jobs in a company.
\begin{center}
\begin{tabular}{|l|l|l|l|l|l|}
\hline
& Job 1 & Job 2 & Job 3 & Job 4 & Job 5 \\
\hline
Alex & 13 & 11 & 9 & 10 & 13 \\
\hline
Bill & 15 & 12 & 12 & 11 & 12 \\
\hline
Cath & 12 & 10 & 8 & 14 & 14 \\
\hline
Don & 11 & 12 & 13 & 14 & 10 \\
\hline
Ed & 12 & 14 & 14 & 13 & 14 \\
\hline
\end{tabular}
\end{center}
It is intended to allocate each applicant to a different job so as to maximise the total score of the five applicants.
\begin{enumerate}[label=(\alph*)]
\item Explain why the Hungarian algorithm may be used if each number, $x$, in the table is replaced by $15 - x$.
\item Form a new table by subtracting each number in the table from 15. Use the Hungarian algorithm to allocate the jobs to the applicants so that the total score is maximised.
\item It is later discovered that Bill has already been allocated to Job 4. Decide how to alter the allocation of the other jobs so as to maximise the score now possible.
\end{enumerate}
\hfill \mbox{\textit{AQA D2 2007 Q2 [13]}}