Date | May 2022 | Marks available | 3 | Reference code | 22M.1.AHL.TZ1.11 |
Level | Additional Higher Level | Paper | Paper 1 | Time zone | Time zone 1 |
Command term | Find | Question number | 11 | Adapted from | N/A |
Question
The matrix has eigenvalues and .
A switch has two states, and . Each second it either remains in the same state or moves according to the following rule: If it is in state it will move to state with a probability of and if it is in state it will move to state with a probability of .
Find an eigenvector corresponding to the eigenvalue of . Give your answer in the form , where .
Using your answer to (a), or otherwise, find the long-term probability of the switch being in state . Give your answer in the form , where .
Markscheme
OR (M1)
(A1)
an eigenvector is (or equivalent with integer values) A1
[3 marks]
EITHER
(the long-term probability matrix is given by the eigenvector corresponding to the eigenvalue equal to , scaled so that the sum of the entries is )
(M1)
OR
(M1)
OR
considering high powers of the matrix e.g. (M1)
THEN
probability of being in state is A1
[2 marks]
Examiners report
In part (a), some candidates could correctly use either or to find an eigenvector but many did not pay attention to the fact that integer values of the eigenvector were required. Some candidates used the method of finding the steady state by finding for some high value of n in part (b) but ignored the fact that they needed to express their answer in rational form. Some did try to convert their calculated answer of 0.467 to but this could only receive partial credit as an exact answer was required.