FA-319 / Numerical aggregation / Member archive

A weighted total is divided by the number of records · case 04

Changing the scale of weights changes the result, or unequal-weight observations are treated as equally influential.

Member previewVariant 4 · 3 implementations · 9 checks per implementation

Case contract

For integer [value, nonnegative weight] pairs, return the exact weighted mean as a reduced Fraction string. Negative weights, no records, or zero total weight return None. Zero-valued observations remain valid.

Why this case matters

Metrics combined across unequal sample counts need a weighted denominator. Scaling all weights should preserve the result; ignoring that invariant produces misleading aggregate summaries.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
unequal weights including zero value	`"24"`	`"16"`	Failed

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