13. The annual birth and death rates per 1000 are 39.4 and 19.4 respectively. The number of
years in which the population will be doubled assuming there is no immigration or
emigration is
(a) 35 yrs. (b) 30 yrs. (c) 25 yrs (d) none of these
please explain with answers
Answer is 35 years
Birth rate is 39.4 per 1000 that is population increases by 3.94% per year
and death rate is 19.4 per 1000 that is population decreases by 1.94% per year
net increase is 2%, now apply compound interest formula
1000 (1 + 0.02)n = 2000
(1.02)n = 2
Now solve this on calculator, and get value of n
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