D2 June 2018 Q1
1. Table 1 shows the cost, in pounds, of transporting one unit of stock from each of four supply points, A, B, C and D, to each of four demand points, 1, 2, 3 and 4. It also shows the stock held at each supply point and the stock required at each demand point. A minimum cost solution to this transportation problem is required.
| 1 | 2 | 3 | 4 | Supply | |
|---|---|---|---|---|---|
| A | 24 | 32 | 21 | 34 | 27 |
| B | 28 | 31 | 29 | 37 | 41 |
| C | 25 | 41 | 33 | 35 | 31 |
| D | 23 | 32 | 31 | 36 | 14 |
| Demand | 33 | 35 | 25 | 20 |
Table 1
Table 2 shows an initial solution given by the north-west corner method.
| 1 | 2 | 3 | 4 | |
|---|---|---|---|---|
| A | 27 | |||
| B | 6 | 35 | ||
| C | 0 | 25 | 6 | |
| D | 14 |
Table 2
Taking the most negative improvement index to indicate the entering cell,
| Scheme | Marks |
|---|---|
| The solution would otherwise be degenerate | B1 |
| B3 | B1 |
| (2) |
Notes
a1B1: ‘degenerate’ or an argument based on \(n + m - 1\) required (values do not need to be substituted) – not just ‘need 7 values’, ‘there are only 6 entries’, ‘so we can do a stepping-stone method’ or ‘demand and supply has been met’
a2B1: CAO (B3) – could be seen in a diagram (but must be clear)
| Scheme | Marks | |||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| M1 A1 A1 | |||||||||||||||||||||||||
| (3) |
Notes
b1M1: Finding 8 shadow costs and 9 IIs
b1A1: CAO for shadow costs [Alt: A(24), B(28), C(38), D(39), 1(0), 2(3), 3(-5), 4(-3)]
b2A1: CAO for improvement indices – must not be stated as part of a table of costs unless clearly differentiated from these costs e.g. circled, underlined, etc.
| Scheme | Marks |
|---|---|
| Route is e.g. D1 – B1 – B2 – C2 – C4 – D4 | M1 |
| Entering cell is D1, Exiting cell is C2 | A1 |
| (2) | |
| 7 marks |
Notes
c1M1: A valid route (possibly drawn so need not be explicitly stated), their most negative II chosen, only one empty square, \(\theta\)’s balanced
c1A1: Correct stepping-stone route stated or clearly shown on a diagram and CAO for entering and exiting cells
SC1: Those candidates who have a 0 in B3 can score (b) M1A0A0 (c) M1A1 – the M in (b) is for finding 8 shadow costs and 9 IIs. The M mark in (c) is for the correct route D1 – B1 – B3 – C3 – C4 – D4 and the A mark is for the correct entering cell (D1) and correct exiting cell (B1)
SC2: Those candidates who have a 0 in C2 for (b) but then move it to B3 for (c) can score full marks in (b) and then M1 only in (c) for a valid balancing route