Question

the population of a city is expected to triple every 25 years . when can the city planners expect the present population of 180 persons to double?

Answer 1

since every 25 years the population grows by a factor of 3,

P(y) = 180*3^(y/25)

2(180) = 180*3(y/25)
2 = 3^(y/25)
ln2 = y/25 ln3
y = 25*ln2/ln3
= 15.77

Answer 2

A population of 500 triples every year. What will the population be after 3 years?