Question

A country's population in 1991 was 136 million. In 2000 it was 141 million. Estimate the population in 2016 using the exponential growth formula. Round your answer to the nearest million. ...?

Answer 1

The answer is 150 million.

Step 1. Calculate the growth rate.
Step 2. Calculate the population number in 2014.

We will use the formula for exponential growth:
A = P * eⁿˣ
where:
A - the final amount (value)
P - the initial amount (value)
e - the mathematical constant (e ≈ 2.72)
n - the growth rate
x - the time

Step 1:
A = 141 million = 141 000 000
P = 136 million = 136 000 000
n = ?
x = 2000 - 1991 = 9
Therefore:
$141 000 000 = 136000 000 * e ^{n*9} \\ e ^{n*9} =141000 000 /136000000 \\ e ^{n*9} =1.04$

Logarithm both sides of the equation:
$ln(e ^{n*9})=ln(1.04) \\ n*9*ln(e) = ln(1.04) \\ 6n=ln(1.04) \\ n = \frac{ln(1.04)}{9} \\ n = \frac{0.04}{9} \\ n = 0.004$

Step 2:
Now when we know the growth rate, it is easy to estimate the population in 2016
A = ?
P = 141 000 000
n = 0.004
t = 2016 - 2000 = 16
$A = 141 000 000 * e ^{0.004*16} \\ A = 141000 000 * e^{0.0640} \\ A = 141000 000 * 1.066\\ A = 150306 000$

Thus, the population will be nearly 150 million in 2016