| Answer | Marks | Guidance |
|--------|-------|----------|
| AC, AB, BH; AF AG; DG, DE or BE | M1 A1 A1 (3) | First three arcs correctly chosen in order {AC, AB, BH,...} or first four nodes correctly chosen in order {A, C, B, H,...}. If any rejections seen at any point then M1 (max) only. Order of nodes may be seen at the top of the matrix {1, 3, 2, -, -, -, 4} so please check the top of the matrix carefully. |
| Weight of tree = 73 (mins) | B1 | |
| No – there are two different MST (with a weight of 73) either with DE or BE | B1 (1) | CAO – mention of two different MST with either arc BE or DE. |
| | 6 marks | |

**Notes for Question 1:**

- a1A1: First five arcs correctly chosen in order {AC, AB, BH, AF, AG,...} or all eight nodes correctly chosen in order {A, C, B, H, F, G, D, E}. Order of nodes may be seen at the top of the matrix so for the first two marks accept {1, 3, 2, 7, 8, 5, 6, 4} (do not condone any missing numbers e.g. the number 8 must be above E).
- a2A1: All arcs correct stated and chosen in the correct order. Candidates must be considering arcs for this final mark (do not accept a list of nodes or numbers across the top of the matrix unless the correct list of arcs (in the correct order) is also seen). Allow DE or BE for the final arc but not DE and BE.
- **Misread**: Starting at a node other than A scores M1 only – must have the first three arcs (or four nodes) correct (and in the correct order).
- b1B1: CAO (condone lack of weights on arcs) – condone, say, a dashed line between B and E if arc DE is in the tree (or vice-versa).
- b2B1: CAO (73) (condone lack of units).
- c1B1: CAO – mention of two different MST with either arc BE or DE.

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