# Three original fictional source cards

All names, offers, quotes and figures are invented for teaching. None describes a real business, school, student or transport system. Keep the source label when sharing a sentence: the point is to notice what information can and cannot support.

## Text A — Repair-club flyer and explainer

**Fictional source:** a draft flyer by the imaginary *Fix-It Club*, with a small-print explainer written by the same club. The club is not a real provider.

> **Flyer headline:** “Join Plan A and save on every repair!”  \
> **Plan A:** $18 joining cost, then $7 for each repair.  \
> **Plan B:** no joining cost, then $10 for each repair.  \
> **Small print:** Prices are model values in Australian dollars. Let `n` be a non-negative whole number of repairs. Total model costs are `A(n)=18+7n` and `B(n)=10n`. No tax, travel, parts, quality, waiting time or eligibility details have been supplied. A real offer would need current conditions checked.

**Teacher note:** Plan A does *not* save at every repair count. At `n=0`, A costs $18 versus B $0. At `n=6`, both cost $60. At integer `n>6`, Plan A has lower model total. “Save on every repair” may mean the marginal charge is $7 versus $10, but readers could reasonably take it to mean the **total** is always lower. That ambiguity is the analytical opening.

## Text B — A post about an invented travel poll

**Fictional source:** a draft post by the imaginary *School Travel Group*.

> “Everyone cycles to school now! We asked 20 students standing beside the bicycle racks on a dry Tuesday. Sixteen said bicycle, one said walk/roll, one bus and two other. That proves 80% of all students cycle. The school should remove the bus-stop shelter.”

**Other information in the same fictional exercise:** the imagined population is 100 students with known model categories: 40 walk/roll, 30 bus, 20 bicycle and 10 other. Two separate *seeded pseudorandom simulations* select 20 of the fictional 100 without replacement: Sample A has 8 walk/roll, 7 bus, 3 bicycle, 2 other; Sample B has 10 walk/roll, 5 bus, 4 bicycle, 1 other. [The exact seeds and method](../mathematics/MATERIALS.md#how-the-simulated-random-samples-were-made) are supplied. These are **not genuine surveys**. The rack sample is a constructed convenience result at a location where cyclists are likely to be overrepresented.

**Teacher note:** the rack claim computes `16/20=80%` correctly **for that sample**, but the selection makes population inference unsound. The known fictional population proportion for bicycle is `20/100=20%`. The recommendation about the shelter is unsupported by these data and could affect students who use the bus. Avoid judging any family's transport choice.

## Text C — A source ledger, not an answer sheet

| Claim | Supplied source | Can the source establish it? |
| --- | --- | --- |
| “At 6 repairs both model plans cost $60.” | Text A formulas | Yes, by substitution, under stated model. |
| “Plan A is best for everyone.” | Text A flyer | No; needs usage, full conditions, priorities. |
| “16 of 20 people by the racks said bicycle.” | Text B post | This is what the fictional post reports; the underlying responses are not independently verified. |
| “80% of all students cycle.” | Rack convenience sample | No. Sample selection does not justify that inference. |
| “Sample A and B gave different bicycle proportions.” | Fictional model table | Yes, 15% and 20%, showing variation in these two constructed samples. |

**Mini glossary for a teacher to adapt:** *substantiation* means evidence that supports a specific claim; *nominalisation* turns a process into a noun (for example “we decided” → “the decision”), sometimes hiding who acted; *population* is the full group a question concerns; *sample* is a subset; *convenience sample* is chosen for ease, not by a fair chance mechanism. Invite everyday/home-language explanations, then teach the precise English term. No translation here has been verified.

**Rights:** Original fictional texts © NeuroForgeIO Pty Ltd 2026, SubjectNest, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); credit, source and changes required.