Edexcel D2 — Question 2 10 marks

Exam BoardEdexcel
ModuleD2 (Decision Mathematics 2)
Marks10
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicDynamic Programming
TypeDynamic programming order sequencing
DifficultyModerate -0.3 This is a standard D2 dynamic programming question requiring systematic backward induction through four stages with minimax optimization. While it involves careful table work and multiple calculations, the algorithm is routine and well-practiced at this level, with no conceptual surprises or proof elements—slightly easier than average due to its mechanical nature.
Spec7.05a Critical path analysis: activity on arc networks7.05b Forward and backward pass: earliest/latest times, critical activities

2. This question should be answered on the sheet provided. A pool player is to play in four tournaments. Some of the tournaments take place simultaneously and the player has to choose one of each of the following: $$\begin{array} { l l } 1 ^ { \text {st } } \text { tournament: } & A , B \text { or } C , \\ 2 ^ { \text {nd } } \text { tournament: } & D , E \text { or } F , \\ 3 ^ { \text {rd } } \text { tournament: } & G , H \text { or } I , \\ 4 ^ { \text {th } } \text { tournament: } & J , K \text { or } L \end{array}$$ Each tournament has six rounds and the player estimates how well he will do in each tournament based on which tournament he plays before it. The table below shows his expectations with each number indicating the round he expects to reach and a "7" indicating he expects to win the tournament.
\multirow{2}{*}{}Expected performance in tournament
ABC\(D\)E\(F\)\(G\)\(H\)IJ\(K\)\(L\)
\multirow{10}{*}{Previous tournament}None533
A637
B554
C755
D533
E356
\(F\)365
G241
H322
\(I\)253
He wishes to choose the tournaments such that his worst performance is as good as possible. Use dynamic programming to find which tournaments he should play.
(10 marks)

Question 2:
AnswerMarks Guidance
Stage 4 (tournament 4): For each previous tournament, find max of \(J, K, L\)M1
After \(G\): \(J=2, K=4, L=1\) → choose \(K\), value 4A1
After \(H\): \(J=3, K=2, L=2\) → choose \(J\), value 3A1
After \(I\): \(J=2, K=5, L=3\) → choose \(K\), value 5A1
Stage 3 (tournament 3): For each previous, find max of \(G+f_4(G), H+f_4(H), I+f_4(I)\)M1
After \(D\): \(G: 5+4=9\), \(H: 3+3=6\), \(I: 3+5=8\) → choose \(G\), value 9A1
After \(E\): \(G: 3+4=7\), \(H: 5+3=8\), \(I: 6+5=11\) → choose \(I\), value 11A1
After \(F\): \(G: 3+4=7\), \(H: 6+3=9\), \(I: 5+5=10\) → choose \(I\), value 10A1
Stage 2 (tournament 2): \(D: 6+9=15\), \(E: 3+11=14\), \(F: 7+10=17\) → choose \(F\)M1 A1
Stage 1: None → \(A: 5+17=22\)... trace back optimal path
Optimal: Play \(A\) (or \(B\) or \(C\)), \(F\), \(I\), \(K\) with minimax value statedA1 ft from working
# Question 2:

| Stage 4 (tournament 4): For each previous tournament, find max of $J, K, L$ | M1 | |
| After $G$: $J=2, K=4, L=1$ → choose $K$, value 4 | A1 | |
| After $H$: $J=3, K=2, L=2$ → choose $J$, value 3 | A1 | |
| After $I$: $J=2, K=5, L=3$ → choose $K$, value 5 | A1 | |
| Stage 3 (tournament 3): For each previous, find max of $G+f_4(G), H+f_4(H), I+f_4(I)$ | M1 | |
| After $D$: $G: 5+4=9$, $H: 3+3=6$, $I: 3+5=8$ → choose $G$, value 9 | A1 | |
| After $E$: $G: 3+4=7$, $H: 5+3=8$, $I: 6+5=11$ → choose $I$, value 11 | A1 | |
| After $F$: $G: 3+4=7$, $H: 6+3=9$, $I: 5+5=10$ → choose $I$, value 10 | A1 | |
| Stage 2 (tournament 2): $D: 6+9=15$, $E: 3+11=14$, $F: 7+10=17$ → choose $F$ | M1 A1 | |
| Stage 1: None → $A: 5+17=22$... trace back optimal path | | |
| Optimal: Play $A$ (or $B$ or $C$), $F$, $I$, $K$ with minimax value stated | A1 | ft from working |

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2. This question should be answered on the sheet provided.

A pool player is to play in four tournaments. Some of the tournaments take place simultaneously and the player has to choose one of each of the following:

$$\begin{array} { l l } 
1 ^ { \text {st } } \text { tournament: } & A , B \text { or } C , \\
2 ^ { \text {nd } } \text { tournament: } & D , E \text { or } F , \\
3 ^ { \text {rd } } \text { tournament: } & G , H \text { or } I , \\
4 ^ { \text {th } } \text { tournament: } & J , K \text { or } L
\end{array}$$

Each tournament has six rounds and the player estimates how well he will do in each tournament based on which tournament he plays before it. The table below shows his expectations with each number indicating the round he expects to reach and a "7" indicating he expects to win the tournament.

\begin{center}
\begin{tabular}{|l|l|l|l|l|l|l|l|l|l|l|l|l|l|}
\hline
\multicolumn{2}{|c|}{\multirow{2}{*}{}} & \multicolumn{12}{|c|}{Expected performance in tournament} \\
\hline
 &  & A & B & C & $D$ & E & $F$ & $G$ & $H$ & I & J & $K$ & $L$ \\
\hline
\multirow{10}{*}{Previous tournament} & None & 5 & 3 & 3 &  &  &  &  &  &  &  &  &  \\
\hline
 & A &  &  &  & 6 & 3 & 7 &  &  &  &  &  &  \\
\hline
 & B &  &  &  & 5 & 5 & 4 &  &  &  &  &  &  \\
\hline
 & C &  &  &  & 7 & 5 & 5 &  &  &  &  &  &  \\
\hline
 & D &  &  &  &  &  &  & 5 & 3 & 3 &  &  &  \\
\hline
 & E &  &  &  &  &  &  & 3 & 5 & 6 &  &  &  \\
\hline
 & $F$ &  &  &  &  &  &  & 3 & 6 & 5 &  &  &  \\
\hline
 & G &  &  &  &  &  &  &  &  &  & 2 & 4 & 1 \\
\hline
 & H &  &  &  &  &  &  &  &  &  & 3 & 2 & 2 \\
\hline
 & $I$ &  &  &  &  &  &  &  &  &  & 2 & 5 & 3 \\
\hline
\end{tabular}
\end{center}

He wishes to choose the tournaments such that his worst performance is as good as possible. Use dynamic programming to find which tournaments he should play.\\
(10 marks)

\hfill \mbox{\textit{Edexcel D2  Q2 [10]}}