Lesson 4D.1.3
4D.1.3 Transportation problems as linear programs Quiz: Pearson Edexcel Further Maths, Unit 40
20 questions
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Lesson 4D.1.3, Transportation problems as linear programs: 20 multiple choice questions for the Pearson Edexcel Further Maths (9FM0), Unit 40: Transportation problems, written with Revision Ninja.
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The 20 questions
-
In the linear programming formulation of a transportation problem, what does the decision variable x_ij represent?
- The number of units sent from source i to destination j.
- The cost of sending one unit from source i to destination j.
- The improvement index of cell (i, j).
- The total supply available at source i.
-
What is the objective of the transportation linear program with cost C_ij?
- Maximise the sum of C_ij x_ij over all cells.
- Maximise the total number of units shipped.
- Minimise the number of occupied cells.
- Minimise the sum of C_ij x_ij over all cells.
-
Which statement describes a source constraint in the transportation linear program?
- The units sent out of destination j equal its demand b_j.
- The cost from source i equals its supply a_i.
- The units sent out of source i equal its supply a_i, so the sum over j of x_ij = a_i.
- The units received at source i equal its supply a_i.
-
What condition must hold for a transportation problem to be balanced?
- Total supply exceeds total demand by exactly one unit.
- Total supply equals total demand.
- Every cost is a whole number.
- The number of sources equals the number of destinations.
-
How is an unbalanced problem with supply exceeding demand made balanced?
- Delete the cheapest source until the totals match.
- Add a dummy destination with demand equal to the surplus and zero costs.
- Add a dummy source with supply equal to the surplus and zero costs.
- Double every demand value.
-
For a problem with 2 sources and 3 destinations, how many decision variables does the linear program have?
- 5
- 9
- 3
- 6
-
Why does a balanced transportation linear program have one redundant constraint?
- The sum of the source constraints equals the sum of the destination constraints, so one constraint is implied by the others.
- Each variable appears in exactly one constraint, so one of them is redundant.
- The objective row can replace one of the constraints.
- Slack variables always reduce the count of constraints by one.
-
How many independent constraints does a balanced transportation problem with 2 sources and 3 destinations have?
- 5
- 4
- 3
- 6
-
Supplies are 20 and 30, and demands are 10, 25 and 15. What is the common total for this balanced problem?
- 45
- 55
- 50
- 60
-
Total supply is 60 and total demand is 50. What is the demand of the dummy destination needed to balance the problem?
- 5
- 10
- 15
- 60
-
How many decision variables does a transportation problem with 4 sources and 4 destinations have?
- 8
- 20
- 12
- 16
-
A source A has supply 15 and source B has supply 25; destinations X and Y each need 20. Costs: A to X 2, A to Y 5, B to X 4, B to Y 1. What is the cost of the allocation A to X 15, B to X 5, B to Y 20?
- 75
- 65
- 70
- 90
-
In the example with supplies A = 15, B = 25 and demands X = 20, Y = 20, which constraint is x_BX + x_BY = 25?
- The objective function.
- The supply constraint for source B.
- The demand constraint for destination X.
- The demand constraint for destination Y.
-
In the same example with supplies A = 15, B = 25 and demands X = 20, Y = 20, what is the demand constraint for destination X?
- x_AY + x_BY = 20
- x_AX + x_BX = 15
- x_AX + x_BX = 20
- x_AX + x_AY = 20
-
In that same example, what is the total supply?
- 40
- 35
- 50
- 45
-
Why are the optimal flows of a transportation problem with integer supplies and demands whole numbers?
- The constraint matrix is totally unimodular, so every vertex of the feasible region has integer values.
- The costs are integers, so the solution must be integer.
- Every variable is restricted to the values 0 or 1.
- The simplex method always rounds the answer to the nearest integer.
-
A non-degenerate basic feasible solution of a balanced 3 by 3 transportation problem has how many basic (occupied) variables?
- 9
- 5
- 6
- 3
-
Why is the cost of a dummy destination set to zero?
- So that the dummy has the largest possible improvement index.
- So that the dummy has no demand at all.
- Units assigned to the dummy are not really shipped, so they should not add cost.
- So that the objective row becomes all zeros.
-
If every cost in one source's row is increased by 2, does the optimal allocation change?
- Yes, the cost of every allocation doubles.
- No, because every allocation from that source is increased by the same total, so the best allocation is unchanged.
- Yes, the allocation always moves towards that source.
- No, but the objective becomes a maximisation.
-
Which statement about the non-negativity condition x_ij ≥ 0 in the transportation linear program is correct?
- Each x_ij must be an integer between 0 and 1.
- Units cannot be negative, so every variable must be at least zero.
- Unoccupied cells must have negative values.
- The variables must sum to zero across the table.
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