Goal: audit three Card G budget what-ifs with one visible formula and check a numerical constraint. 25 = 2 + 5 + 6 + 7 + 5.
- 0–2: Ask which inputs change by fictional week and which formula stays fixed. No one provides personal data.
- 2–7: Model Week A
1260−680−220−110=$250unassigned; reverse check680+220+110+250=1260. - 7–13: Learners calculate Week B
$205and Week C$245, then check each against the invented at least $200 constraint. Show where a spreadsheet could repeat=income-fixed-essential-discretionary; a paper table is equivalent for arithmetic. - 13–20: Routes: budget counters and a $200 boundary strip; budget map for each week; optional local what-if spreadsheet or typed/paper table with the same formula and a manual spot check. Every route reports all three values, one reverse check and an assumption limit. Actual spreadsheet use is documented separately.
- 20–25: Exit “If Week B food rises $10 alone, what happens?” Key: unassigned falls from $205 to $195, failing the stated model threshold. Move: if a student edits multiple cells, freeze unchanged inputs and subtract the one new $10.
Alternative domain: Invented stage-prop materials plan. Optional/home: change just one made-up cost by $5 and predict the balance; no family budget.