A modelling cycle is more than calculation: formulate → represent → solve → interpret → review. State what quantities vary, their units, and whether a proportional/constant-rate assumption is justified.
Equivalent ratios multiply or divide every part by the same non-zero factor. Rate models may be direct (e.g. constant speed) or include fees/brackets that break simple proportionality. If a phone plan has a fixed fee, “cost per unit” alone may not predict total cost for every usage level.
Preserve the authored elaborations: map/plan scales and mixtures, magnification, exchange-rate travel budgeting, taxation/pay/phone-plan comparisons, radiocarbon ratio contexts used to study long-term human habitation, and First Nations string/cordage ratio applications. Present cultural contexts respectfully and as mathematical applications, not decorative references.