Compare the rule with concrete cases
Fictional pages and minutes_per_page are nonnegative integers; estimate is their product. The record starts with four pages and five minutes each, total twenty. Changing pages to six gives thirty; changing rate to seven on the original gives twenty-eight. These are estimated minutes, not actual work logs.
| Case | Pages | Minutes per page | Expected estimate |
|---|---|---|---|
| Original | 4 | 5 | 20 |
| Page edit only | 6 | 5 | 30 |
| Rate edit only | 4 | 7 | 28 |
Work through the distinction
A page-only test cannot show whether the rate is a declared dependency. Retain a separate actual-minutes field so recalculating an estimate does not rewrite observations.
Both inputs become six pages at seven minutes. What estimate is required?
Show the worked answer
Forty-two minutes: 6×7. Any recorded actual minutes remain unchanged.
Acceptance wording to adapt
Recompute estimated_minutes=pages×minutes_per_page whenever either input changes. Do not accept a stale previous estimate, and preserve actual_minutes on estimate-input edits.