• some students forgot to put in an extra arc (of zero flow) to the degenerate initial basic feasible solution to make it a spanning tree.
• a lot of students used notations that they did not define or explain. Many did not follow the format given in the course outline.
• once one of the dual variables is chosen arbitrarily, the others should be calculated using the formula of zero reduced costs.
• most students failed to economically interpret the dual variables

Q#17 was in general poorly done.

• the values of the dual variables given in the question are incorrect. This might have caused some confusion, though the errors should not directly affect the solutions.
• the biggest problem lies in part (d), where almost no students got all the correct answers. I approach the problem by adding a new node to the original graph to take care of the supply/demand shortage/surplus, and then I calculate the amount of surplus or shortage necessary to alter the spanning tree that corresponds to the original optimal solution. Very few students followed this approach

Consistent with the previous assignments, the other two questions were not marked. 10 marks are awarded to each whenever the question seems to be reasonably attempted.