LET’S TRY ONE
A town starts with 1,000 people. There are 30 births and 10 deaths, with no migration. What is the ending population?
1,020
1,000 + 30 − 10 = 1,020.
Learning steps & teaching tips
Calculate change in an invented population from births, deaths and migration without treating all growth as one cause.
- Separate each flow into additions or removals.
- Calculate natural change and net migration separately.
- Combine the flows and state the limits of the simplified model.
Try it together
Build a one-year population ledger for an invented town. Swap one flow with a partner and recompute the result without changing the other entries.
Start population + births − deaths + arrivals − departures gives the ending population in this model.