Essential skills in a multi-step practical model
| English | 中文 | Pinyin |
|---|---|---|
| model parameter/ˈmɒdl pəˈræmɪtə/ | 模型参数 | mó xíng cān shù |
| model assumption/ˈmɒdl əˈsʌmpʃn/ | 模型假设 | mó xíng jiǎ shè |
A decision before an answer
- A delivery model C=8+3d charges a fixed amount even at zero distance. Treating it as direct proportion changes the problem.
- Your goal: Build a model connecting quantities, rates and geometric measures.
Read the relationship
- Define variables with units and translate each part of the situation. A fixed fee plus a rate gives C=b+md; direct proportion C=md applies only when the intercept is zero. Ratios compare quantities in a chosen order, and successive percentage changes multiply their changing bases. A model should preserve those relationships before any arithmetic begins.
- Interpret parameters and test the model’s assumptions.
C=5+2d. For d=7, C is:
Fixed fee 5 plus 2·7=19.
Use the defining rule
- Convert units by multiplying factors that cancel. For scale models, length factors square for area and cube for volume when every dimension is scaled. Combining a geometric formula with a unit price can model material cost; for example, paint area times cost per square metre gives currency, while using wall volume would have the wrong physical meaning.
- Evaluate predictions and adjust a parameter using new evidence.
Every prediction is 3 units too low across several distances. First adjustment to inspect:
A constant offset suggests the fixed contribution is low.
Check the conditions
- Interpret and test the model. Ask whether a constant rate is plausible across the domain, whether a fixed charge is already included and whether an estimated area excludes doors or overlap. Compare a prediction with observed data and identify which assumption or parameter may need revision. A model’s neat algebra does not establish that it fits reality.
- Evaluate predictions and adjust a parameter using new evidence.
Original delivery model C=8+3d, d in kilometres, predicts 23 units for 5 km. Bills are consistently 2 units higher at several distances, supporting a revised intercept 10 while keeping slope 3. A wall 4 m by 2.5 m has area 10 m²; subtracting a 2 m² doorway gives 8 m² to paint. At 6 units/m², cost is 48. A 1:50 plan of a 4 m wall shows 8 cm.
A 3 m length on a 1:100 plan is ____ cm.
3 m=300 cm, divided by 100.
Apply the task format
- Improve a model by adjusting the parameter supported by evidence. If every predicted bill is exactly two units low, revising the fixed fee may fit better than changing the per-distance slope. A trend in errors with distance points toward the rate instead. Keep modelling as an overlapping activity across content areas, not a separate extra block of official questions.
- Evaluate predictions and adjust a parameter using new evidence.
Do not treat an intercept model as direct proportion or adjust every parameter when evidence identifies one systematic error.
Which answer fits this case?
Build a model connecting quantities, rates and geometric measures
Modelling is counted only in a separate block of enhanced ACT math items.
It overlaps other reporting categories.
Keep the distinctions
- model parameter 模型参数 — A quantity setting a rule’s rate, scale or fixed contribution.
- model assumption 模型假设 — A condition under which the representation is intended to work.
- Build a model connecting quantities, rates and geometric measures.
- Interpret parameters and test the model’s assumptions.
- Evaluate predictions and adjust a parameter using new evidence.
Match each term with its precise meaning in this lesson.
Keep the distinctions stated in the teaching example.
Put this lesson’s reasoning or event sequence in order.
The order follows the stated process; check each stage before the next.