SOLUTION: The world population doubles every 35 years. In 1980 the population wasx 4.5 billion. Assuming that the doubling period remazins at 35years, estimate the population in the year 212

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Question 1170810: The world population doubles every 35 years. In 1980 the population wasx 4.5 billion. Assuming that the doubling period remazins at 35years, estimate the population in the year 2120. SHOW WORK
Found 2 solutions by Boreal, ikleyn:
Answer by Boreal(15235)   (Show Source): You can put this solution on YOUR website!
A=Ao(1+r)^35, r is the rate. A/Ao=2, since it is doubling.
2=(1+r)^35
ln both sides
ln2=35*ln(1+r)
0.0198=ln(1+r). Don't round
raise both sides to the e power
1.02000=1+r
r=2.0%
Consistent with rule of 70, which is 70/2%=35 years to double
2120 is 40 years
A=(1.02)^40*4.5 to get answer
=9.936 billion.
Answer by ikleyn(52864)   (Show Source): You can put this solution on YOUR website!
.

            Tutor @Boreal misread the problem and produced incorrect solution and answer.
            See the correct solution below. 


There are 140 years from 1980 to 2120  (2120 - 1980 = 140).


140 years comprise 4 (four) doubling periods.


Therefore, the prediction for the Earth population in  2140 is


     =  = 72 billions.     ANSWER

Solved.

----------------

See the lesson
    - Population growth problems
in this site.


Also,  you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.

The referred lesson is the part of this online textbook under the topic "Logarithms".


Save the link to this online textbook together with its description

Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson

to your archive and use it when it is needed.



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