6 The network shows the roads linking a warehouse at \(A\) and five shops, \(B , C , D , E\) and \(F\). The numbers on the edges show the lengths, in miles, of the roads. A delivery van leaves the warehouse, delivers to each of the shops and returns to the warehouse.
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- Complete the table, on the page opposite, showing the shortest distances between the vertices.
- Find the total distance travelled if the van follows the cycle \(A E F B C D A\).
- Explain why your answer to part (b)(i) provides an upper bound for the minimum journey length.
- Use the nearest neighbour algorithm starting from \(D\) to find a second upper bound.
- By deleting \(A\), find a lower bound for the minimum journey length.
- Given that the minimum journey length is \(T\), write down the best inequality for \(T\) that can be obtained from your answers to parts (b), (c) and (d).
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\section*{Answer space for question 6}
REFERENCE | \(\boldsymbol { A }\) | \(\boldsymbol { B }\) | \(\boldsymbol { C }\) | \(\boldsymbol { D }\) | \(\boldsymbol { E }\) | \(\boldsymbol { F }\) |
| \(\boldsymbol { A }\) | - | 7 | | | | |
| \(\boldsymbol { B }\) | 7 | - | 5 | | | |
| \(\boldsymbol { C }\) | | 5 | - | 4 | | |
| \(\boldsymbol { D }\) | | | 4 | - | 6 | |
| \(\boldsymbol { E }\) | | | | 6 | - | 10 |
| \(\boldsymbol { F }\) | | | | | 10 | - |