This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Demography and family planning, Subject name: Social & Preventive Medicine
If annual growth rate of a population is 1.5-2%, what number of years will be required to double the population 
Select and explain. 
A. 70-47 years, B. 35-47 years, C. 35-28 years, D. 28-23 years
B: 35-47 years
Answer: B: 35-47 years 
Explanation: When crude death rate is substracted from crude bih rate , the net residual is current annual grow rate , exclusive of migration. When the annual growth rate of a population is 1.5% to 2.0%, it takes 35-47 years to double the size of population. Reference : Park&;s textbook of preventive and social medicine, 23rd edition, pg no: 481, table 5