D1 June 2012 Q5
5.
Figure 4 shows a network of roads. The number on each arc represents the length, in miles, of the corresponding road.
Due to flooding, the roads in and out of D are closed.
| Scheme | Marks |
|---|---|
 | M1 A1(SCFA) A1ft (BD) A1(ET) |
| SCFBDET; length 65 | 1B1; 2B1ft |
| (6) |
Notes
a1M1 Big replaced by smaller at least once at B or D or E or T.
a1A1 S, C, F and A boxes all correct, condone lack of 0 in A’s working value
a2A1ft B and D ft correctly. Penalise order of labelling only once per question.
a3A1 E and T correct. Penalise order of labelling only once per question.
a1B1 Route CAO
a2B1ft their final value ft.
| Scheme | Marks |
|---|---|
| E.g. 65 – 20 = 45 ET; 45 – 12 = 33 DE; 33 – 10 = 23 BD; 23 – 9 = 14 FB; 14 – 6 = 8 CF; 8 – 8 = 0 SC Or Work back from T, including arc XY if the weight of arc XY = the difference in the final values of X and Y. | B2ft, 1ft, 0 |
| (2) |
Notes
b1B1ft Attempting an explanation, at least 3 stages or one half of general explanation.
b2B1ft Correct explanation – all stages, both halves of explanation
Amplification for (b)
General explanation:
1B1 for partial explanation e.g. ‘working backwards/traceback’ or ref to arcs and final value differences
2B1 for working backwards from T + include an arc XY if weight of XY = final value of Y – final value of X.
Demonstration:
1B1 for three correct calculations for their network
2B1 for all calculations correct and linking arcs/nodes to those calculations. Arc lengths and final values visible.
| Scheme | Marks |
|---|---|
| SCFBET; length 68 | B1; B1 |
| (2) | |
| (10 marks) |
Notes
c1B1 Route CAO.
c2B1 length CAO.