Let the population at any instant (t) be y.

Now it is given that the rate of increase of population is proportional to the number of inhabitants at any instant.

Now, integrating both sides, we get,

log y = kt + C ------(1)

According to given conditions,

In the year 1999, t = 0 and y = 20000

⇒ log20000 = C ----(2)

Also, in the year 2004, t = 5 and y = 25000

⇒ log 25000 = k.5 + C

⇒ log 25000 = 5k + log 20000

--------(3)

Also, in the year 2009, t = 10

Now, substituting the values of t, k and c in equation (1), we get

logy =

⇒ y = 31250

Therefore, the population of the village in 2009 will be 31250.