AQA D2 2007 January — Question 2 13 marks

Exam BoardAQA
ModuleD2 (Decision Mathematics 2)
Year2007
SessionJanuary
Marks13
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicMatchings and Allocation
TypeHungarian algorithm for maximisation
DifficultyModerate -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.
Spec7.04a Shortest path: Dijkstra's algorithm

2 Five successful applicants received the following scores when matched against suitability criteria for five jobs in a company.
Job 1Job 2Job 3Job 4Job 5
Alex131191013
Bill1512121112
Cath121081414
Don1112131410
Ed1214141314
It is intended to allocate each applicant to a different job so as to maximise the total score of the five applicants.
  1. Explain why the Hungarian algorithm may be used if each number, \(x\), in the table is replaced by \(15 - x\).
  2. 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.
  3. 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.

Question 2:
Part (a)
AnswerMarks Guidance
AnswerMarks Guidance
Hungarian algorithm minimisesE1
\(15 - x\) gives measure of criteria NOT met, which need minimising in order to maximise scoresE1 Idea of high becoming low, etc. Total: 2
Part (b)
AnswerMarks Guidance
AnswerMarks 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 correctA1
Zeros can be covered with only 4 lines, so adjustment neededE1 Augmented array shown
Reduction by subtracting 1 from each uncovered elementM1
And adding 1 to each element at intersection of two linesA1
Matching on particular zerosM1
\(\text{Alex} \leftrightarrow 5\), \(\text{Don} \leftrightarrow 3\), \(\text{Bill} \leftrightarrow 1\), \(\text{Ed} \leftrightarrow 2\), \(\text{Cath} \leftrightarrow 4\)A1 If adjustment not done correctly and matching made, award B1 for 3 correct and B1 for rest correct. Total: 8
Part (c)
AnswerMarks Guidance
AnswerMarks Guidance
Deleting row 2 and column 4 either in final matrix or reworkingM1
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** |

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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]}}