**The brief.** Four movement reports. Each has an opening balance, some causes, and a closing balance. Each one ties. **Exactly one of them ties because a line was made to absorb the remainder.** Find it — and say what gave it away.
A plug is not always labelled "unexplained". It hides in a line with a plausible name, and the only reliable tell is structural: a plug is the line that would change to whatever value it had to, if any other number moved.
The rules
- Every report below balances. Balancing is not evidence of anything.
- Work out which line is not independently determined — the one defined by the others rather than by something that happened.
- Two of the reports contain a genuinely small residual line that is not a plug. Say why it isn't.
Your workbench
Fill in plugReport and plugLine. The battery ships red — two checks, both failing.
Made your call? Reveal the solution.