A developing country has a current annual population growth rate of 2 percent. Using the rule of 70, approximately how many years will its population take to double?
- A 70 years
- B 50 years
- C 35 years ✓
- D 20 years
Correct answer: C. 35 years
Explanation
Doubling time is approximated by dividing 70 by the annual percentage growth rate. With a 2 percent growth rate, doubling time is 70 divided by 2, giving 35 years. This shortcut derives from the compound growth formula and is standard in demography teaching. Option A would apply only if the growth rate were 1 percent per year, and option B corresponds to roughly a 1.4 percent growth rate, values students often confuse when recalling India's recent growth figures.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.