LET’S TRY ONE
A simplified reservoir contains 100 units. During one year, inputs are 12 and outputs 9 units. What is its ending stock?
103 units
100 + 12 − 9 = 103 units.
Learning steps & teaching tips
Use a stated stock-and-flow model to calculate change while distinguishing model assumptions from real-world forecasts.
- Draw the model boundary and name the stored quantity.
- Calculate each interval's net input.
- Test how an assumption changes the projection and explain what the model leaves out.
Try it together
Model a reservoir using tokens. Change one inflow or outflow, compute three intervals, and list a real process that the simplified model does not represent.
Ending stock = starting stock + inputs − outputs; keep all quantities in the same units and time interval.