Model with an Inequality, Then Read the Range
A situation with a threshold -- at least, cheaper than, before the deadline -- becomes a linear inequality in the unknown. The modelling is the same as for an equation; what changes is that the answer is an interval, so the boundary (included or not, rounded which way) decides it, and two thresholds on one situation give a range squeezed from both sides.
grade 7–8 ExpressionsGeometry Convert to AlgebraEliminate Possibilities
Progression (5)
g7 1. One win count sets both players' scores Expressions
g7 2. Moving-point triangle area by subtraction ExpressionsGeometry
g7 3. Average cost under a flat fee plus surcharge Expressions
g7 4. Spend downstream time first, bound upstream speed RatiosExpressions
g7 5. Two thresholds on one mixture give a range ExpressionsRatios