D1 June 2009 Q5
5.

[The total weight of the network is 625 m]
Figure 3 models a network of paths in a park. The number on each arc represents the length, in m, of that path.
Rob needs to travel along each path to inspect the surface. He wants to minimise the length of his route.
The surface on each path is to be renewed. A machine will be hired to do this task and driven along each path.
The machine will be delivered to point G and will start from there, but it may be collected from any point once the task is complete.
| Scheme | Marks |
|---|---|
| CD + EG = 45 + 38 = 83 | M1 1A1 |
| CE + DG = 39 + 43 = 82 ← | 2A1 |
| CG + DE = 65 + 35 = 100 | 3A1 |
| Repeat CE and DG | 4A1ft |
| Length 625 + 82 = 707 (m) | 5A1ft |
| (6) |
Notes
(a) 1M1: Three pairings of their four odd nodes
1A1: one row correct
2A1: two rows correct
3A1: three rows correct
4A1ft: ft their least, but must be the correct shortest route arcs on network. (condone DG)
5A1ft: 625 + their least = a number. Condone lack of m
| Scheme | Marks |
|---|---|
| DE (or 35) is the smallest | M1 |
| So finish at C. | A1ft |
| New route 625 + 35 = 660 (m) | A1ft=1B1 |
| (3) | |
| (9 marks) |
Notes
(b) 1M1: Identifies their shortest from a choice of at least 2 rows.
1A1ft: ft from their least or indicates C.
2A1ft = 1Bft: correct for their least. (Indept of M mark)