What is the doubling time?

Question

The population of a region is growing exponentially. There were 25 million people in 1980 and 80 million people in 1990. Find an exponential model for the population (in millions of people) at any time , in years after 1980. What is the doubling time?

Answer 1

80 = 25e^kt

3.2 = e^10k

ln 3.2 = 10k

0.11635 = k

2 = e^0.11635t

ln 2 = 0.11635t

0.693147 = 0.11635t

5.9574 = t