Plan from the supplied facts
Fictional rigid design costs two hours now and eight extra if a later rule changes. Flexible design costs five now and one extra if it changes. Supplied change probability is 0.5, with no other costs or benefits. Compare expected total effort, not the cheapest unchanged outcome.
| Design | No change h | Change h | Expected h at p=.5 |
|---|---|---|---|
| Rigid | 2 | 10 | 6 |
| Flexible | 5 | 6 | 5.5 |
| Difference | Rigid 3 less | Flexible 4 less | Flexible .5 less |
Work through the choice
Expected totals are 2+0.5×8=6 and 5+0.5×1=5.5. A flexible design is not always lower effort: if no rule changes, it costs three more.
If the supplied change probability is zero, which design has lower effort?
Show the worked answer
Rigid at two hours versus flexible at five. The choice depends on the supplied uncertainty model.
Material to use in your plan
List initial effort, revision effort and the change probability for each design. Retain both conditional outcomes alongside the expected total and the reasons for the probability assumption.