Question

In 1951, the population of India was 357 million people. By 1981 it had grown to 984 million. If the population is growing exponentially, when (in what month of what year) will the population reach 1 billion people?

Answer 1

let the equation be

P = 357(e)^(kt) where t is the time in years since 1951

so 1981 ---> t = 30

984 = 357(e^30k)
2.756303 = e^30k
30k = ln 2.756303
k = .0337963

so now we have P = 357(e^.0337963t)

so 1000 = 357(e^.0337963t)
2.80112 = e^.0337963t
t = 30.477
30 years + .477 of the next year
30 yrs + 5.7 months
or
in the 6th month of 1951

Answer 2

wouldn't it be past 1981 instead of in the 6th month of 1951?

Answer 3

of course, clearly a typo. Sorry about that.

since my t=30.477 and I defined as 1951 as t=0
the time is 1951 + 30.477 = 1981 + .477yrs.

Answer 4

Does the .477 years mean the 6th month (June) you were talking about?