What is the 3-unit growth/decay factor?

Question

The population of Northfield, New Jersey is expected to increase by 1.8% every three years. The population of Northfield in 2012 was 8,624 people. Let n be the number of years since 2009.

Answer 1

grows 1.8% in 3 years

that's about 1.8/3 = about 0.6% growth rate in 1 year

8624 = Poe^.018/3

Po = 8624e^-.006 = 8470.16 in year 0

but population growth while close to continuous is less so

8624/8470.16 = (1+r)^3

1+r = cube root of 824/8470.16 = about .602% maximum annual growth rate

.6% < growth rate < .602%