A Growth at a rate of 2.5% may seem slow but this means a country GDP will double within 28 years. 100 (1+0.

A Growth at a rate of 2.5% may seem slow but this means a country GDP will double within 28 years. 100 (1+0.025)^28 = 200 if the growth rate is 3% then the economy will double its production within 24 years....I don't understand this or how I actually would go about calculating the economic growth rate? Also, Do economies converge??Thank you!!