SOLUTION: how long will it take for the population of a certain country to double if its annual growth rate is 3.3%? round to the nearest year. i got 21 and 9 years my freind got 6

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Question 241258: how long will it take for the population of a certain country to double if its annual growth rate is 3.3%? round to the nearest year.

i got 21 and 9 years
my freind got 61 and 1
which is correct? :)
Found 2 solutions by stanbon, rfer:
Answer by stanbon(48545) (Show Source):
You can put this solution on YOUR website!
how long will it take for the population of a certain country to double if its annual growth rate is 3.3%? round to the nearest year.
---------------------------------
2P = Pe^(rt)
e^(0.033t) = 2
Take the natural log:
0.033t = 0.693147...
t = 21.0 years

Answer by rfer(10417) (Show Source):
You can put this solution on YOUR website!
Just using the rule of 72, I get 21.8 yrs.
That methode is not exact, but close.