# AQA Decision 1 January 11 Question Error?

Discussion in 'Mathematics' started by bbibbler, Mar 24, 2011.

1. ### bbibblerNew commenter

I cannot see how it could ever equal 3 factorial.
Are you sure that the last part of the question is not a Travelling Salesman problem?.

I do not have the paper, so I am just guessing/musing.

2. ### rachie_j

The Question is definately Chinese Postman. Its a network with 8 vertices, 4 are odd (A,G,B,H).
Part A says give a reason why it is not possible to start at A, walk along each street once and return to A- clearly because network contains odd vertices, therefore not Eularian.
Part B is find the length of an optimal chinese postman route starting and finishing at A. Best pairing of odd vertices is AG and BH which adds into the network to give the correct total.
Part C is for an optimal chinese postman route state;
i) the number of times that the vertex F would occur. F has order 4 and is not changed by the chinese postman problem and so should be visited twice.
ii) the number of times that the vertex H would occur. H had order 3 but the extra makes it 4 therefore its visited twice as the mark scheme states.
Hope this makes sense! The question is driving us all at my school mad as we cannot think why it would be 3!

4. ### rachie_j

I get it!!! I am so thick- it was so obvious!
The extra bits you add in are AG and BH but the shortest route from B to H is through F and so it now has order 6 which means it is visited 3 times.
I hate it when Decision gets me like that, not slept in days trying to work it out!

5. ### weebecka

!!!!! that's worrying rachie_j

(sorry, the post above was a complete accident).

6. ### Polecat

The Principal Examiner for AQA Decision usually sets questions based on the data from his last holiday abroad. Not sure if this applies here.