Date | May 2021 | Marks available | 3 | Reference code | 21M.1.AHL.TZ2.13 |
Level | Additional Higher Level | Paper | Paper 1 | Time zone | Time zone 2 |
Command term | Estimate | Question number | 13 | Adapted from | N/A |
Question
The graph below shows a small maze, in the form of a network of directed routes. The vertices to show junctions in the maze and the edges show the possible paths available from one vertex to another.
A mouse is placed at vertex and left to wander the maze freely. The routes shown by dashed lines indicate paths sprinkled with sugar.
When the mouse reaches any junction, she rests for a constant time before continuing.
At any junction, it may also be assumed that
- the mouse chooses any available normal path with equal probability
- if the junction includes a path sprinkled with sugar, the probability of choosing this path is twice that of a normal path.
Determine the transition matrix for this graph.
If the mouse was left to wander indefinitely, use your graphic display calculator to estimate the percentage of time that the mouse would spend at point .
Comment on your answer to part (b), referring to at least one limitation of the model.
Markscheme
transition matrix is M1A1A1
Note: Allow the transposed matrix.
Award M1 for a matrix with all values between and , and all columns (or rows if transposed) adding up to , award A1 for one correct row (or column if transposed) and A1 for all rows (or columns if transposed) correct.
[3 marks]
attempting to raise the transition matrix to a large power (M1)
steady state vector is (A1)
so percentage of time spent at vertex is A1
Note: Accept .
[3 marks]
the model assumes instantaneous travel from junction to junction, R1
and hence the answer obtained would be an overestimate R1
OR
the mouse may eat the sugar over time R1
and hence the probabilities would change R1
Note: Accept any other sensible answer.
[3 marks]