The population of a city is growing at an average rate of 3% per year. In 1990, the population was 45,000. Determine the year during which the population will have doubled.

45000 * 1.03^t = 90000

1.03^t = 2

t*log (1.03) = log (2)

t = log (2) / log (1.03) = 23.44977 ...

This means that the population would have doubled in 23.44 years i. e. roughly in the middle of 2013, so it will first have exceeded 90000