How would you write this into an equation?

Question

If we were trying to make a prediction of the population of a town in the year 2020 the equation could look like

Answer 1

let CC = Current population(2007,2008....)
PP = Predicted Population(2020)
AG1-AG13 = Average Growt rate per year (2020-2007=13)

PP = Summation(CCn*AGn)

Note : the eqn does not contain Death rate

Answer 2

. . . or exponential growth:
P=Po e ^at

Future population equals present population times "e" raised to the (growth per period) times (periods to reach the future time)

Answer 3

Population_year_2020 = Current_population + births - deaths + new citizens + illegal immigrants - people who move away