Lately I have been doing some numeracy tests in order to prepare myself for a test based interview as it seems to be the case with some of the firms hiring these days. Here is the question. I can not get my head around it. In fact I can get the answer doing it manually, but I think there a mathematical formula available to work this kind of problems out. Thanks a lot.

A town with a population of 2000 grows at a rate of 30% per annum. What will be its population in the next 4 years?