OpenStax
Read source ↗Writing, Graphing, and Solving a Linear Equation
Supports representing a starting amount plus a constant savings rate with a linear equation. It does not supply ILP's dollar values or goal.
Experiment 02 · 2–4 minutes
One plan, four horizons
Move between four time lenses, change one weekly input, and watch the same savings model redraw across the long range.
Options
About this experiment
Use it: Choose a time lens, then change the weekly amount. The entire trajectory redraws immediately.
Read it both ways: Trace forward from the weekly input or backward from the laptop goal. The underlying model does not change.
Boundary: This is a fixed authored arithmetic model, not a live forecast or financial guidance.
One input · one trajectory · four time lenses
When does $10 a week become enough for a $2,500 laptop?
Start with $100. Pick a horizon, then change the amount saved each week and watch every point respond.
Fixed arithmetic model · not a forecast or financial guidance
View at
Change one input
Save each week
All four horizons update. The $100 start and $2,500 goal stay fixed.
Projected savings$10 / week
Milestone view · intervals are labeled, not drawn to scale
Start$100
At one month, this plan reaches $140.
$2,360 still to go. $100 to start plus $10 each week for 4 weeks gives $140 at one month.
Explain this selected point
Same model · two directions
Trace what drives this result
Start$100→Weekly$10 / week→1 month$140→Goal$2,500
$10 / week carries the $100 start to $140 at 1 month.
Try at least two horizons and one other weekly amount to compare the projection.
Sources and boundariesThe relationship is transparent. The scenario is authored.Open details
OpenStax shows how a starting amount and constant rate can be represented with a linear equation, and why a model has a limited domain. It does not supply this laptop price, savings plan, or projection.
OpenStax
Read source ↗Modeling with Linear Functions
Supports constant-rate linear modeling and the need to limit a model to the conditions where its assumptions remain reasonable.
Limitations and open questions
- The scenario, dollar values, price, and time lenses are authored for this learning instrument.
- The model assumes the same deposit arrives every week and ignores interest, withdrawals, missed deposits, fees, taxes, and price changes.
- The five-year line is a conditional projection, not a claim that real finances remain constant for five years.
- The instrument does not adapt automatically, infer intent, or generate content. Detail is opened by the learner.