The city of Marietta is currently debating the future of the old Armory building on Front Street. Suppose that the mayor has proceeded with his plans to refurbish the building and use it as a transportation hub and visitor center. The estimated cost to complete the museum was initially $1.6 million. The mayor also believes that the transportation hub will generate an estimated benefit of $2.4 million.
The benefit estimate appears to be correct, but costs to date total $2.7 million, and the transportation hub still is not ready. The cost of completing the transportation hub, X, is uncertain.
City Council member Flintstone wants to stop now: "Whatever the value of X, it is clear that the transportation hub will yield negative net benefits." Council member Rubble wants to continue: "If we stop now, we will have wasted $2.7 million."
Comment. How should the decision depend on the value of X?
Congratulations to Kaitlin Huck for being the first of three to submit a correct answer. Using marginal analysis, the decision on whether to continue the project or not hinges on the value of X, the cost of completing the project. The $2.7m costs to date are sunk costs and should not affect the decision to continue or stop the project.