EXD.2:4.3 - Vary the condition that matters

Choose a changed case that distinguishes the intended relation from the plausible alternative. Ask what should stay the same, what should change and why. Keep irrelevant complexity low enough for the relation to remain visible.

Inspect the rule as well as the number. Equal group counts allow an unweighted average of the group means to agree with the pooled mean. Equal group means can also make the two numerical answers coincide despite unequal counts. The governing target still determines which weighting rule the explanation should express.

Use EXD.5 when a recipient’s own account and supported correction serve a learning purpose. Use EXD.4 when the response changes the question, premise or next explanation.