# Reference answer and acceptance criteria

| Period | Included document IDs | Net total PLN |
|---|---|---:|
| 1–7 October 2026 | FV-001, FV-002, FV-003 | 3000 |
| 8–14 October 2026 | FV-004, FV-005 once, FV-006, KOR-009 | 3400 |

Difference: 3400 − 3000 = 400 PLN. Change: 400 / 3000 × 100% = 13.33%, rounded to two decimal places.

Exclusions: the second FV-005 is an identical duplicate (1800 PLN); OF-007 is a draft proposal (900 PLN); FV-008 is 400 EUR, reported separately without a conversion rule. KOR-009 is included at −200 PLN.

Acceptable commentary: “The value of documents included under the agreed PLN definition increased by PLN 400, or 13.33%. The duplicate, draft proposal and EUR 400 document are excluded from that total. The data does not establish the cause of the increase.”

## Why the bad answer looks plausible

6500 = 3400 + duplicate 1800 + draft 900 + foreign-currency amount 400. The arithmetic can be correct while the selected inputs are wrong. 116.67% follows consistently from that wrong total. Checking only the formula will not fix it.

There is no campaign spend, acquisition-channel data or experiment in the file. A marketing explanation and a 20% budget increase are unsupported.

## Self-assessment: 10 points

Give 0, 1 or 2 points for each item: 0 missing/wrong; 1 partial; 2 fully met.

1. Correct periods, status and currency.
2. Duplicate counted once; negative adjustment included.
3. Both totals, difference and percentage with the right denominator.
4. Explicit exclusions and source document IDs.
5. No invented cause; concise readable report.

Target: at least 8 points and no incorrect total, mixed currencies or unsupported cause. A critical error requires correction regardless of points. This is a learning rubric, not a validated competence assessment.

## Scenario question

The percentage formula is correct but the report shows PLN 6500. What should you check first?

A. Increase reasoning effort and repeat the same request.
B. Check input records: duplicates, statuses and currencies.
C. Round the percentage to a whole number.

B. A stronger model does not automatically fix an undefined metric. Rounding changes presentation, not the cause of the error.

## Second trial

With FV-006 = 800 PLN: second-period total 3600 PLN, difference 600 PLN, increase 20%. Exclusions are unchanged; the new amount does not establish a cause.

## Advanced trial

Remove the FV-006 amount. A blank is not zero. The known part of the second period is 2800 PLN, but the full total and percentage change cannot be determined until the missing amount is supplied. Asking a question is the correct outcome here.