Posted by **Erika** on Friday, November 5, 2010 at 12:17am.

for population in billions, where t is years since 1990:

N(t) = 41/1+11 e^−0.1 t

(b) According to this model, when will the earth's population reach 20.5 billion?

During the year .

How about 40.9 billion?

During the year .

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