[Math] Exponential Growth

calculusexponential function

I'm trying to wrap my head around the algebra used to get a solution.
The question states:

In 2011, the Population of China and India were approximately 1.34 and 1.19
billion people, respectively. However due to central control the
annual population growth rate of China was 0.4% while the population
of India was growing by 1.37% each year. if these growth rates remain
constant. when will the population of India exceed that of China?

  • 2023

So the general formula would be $P = P(not) A^{kt}$
so I've tried
$1.34 = 1.19e^{0.0137t}$
—divide by 1.19 on both sides and take ln of both sides
$\ln(1.34/1.19) = 0.0137t$.
I, quiet cluelessly, divided by 0.0137 on both sides but that of course would give me an erroneous solution.

I generally understand exponential growth, or at least the idea behind how to calculate certain values, but this question in particular I haven't quiet understood.
I would appreciate any help on how to go about correctly finding the correct value of t (2023). I'm sure my algebra skills are at fault

Best Answer

So the growth function for the population of China is $C(t)=1.34(1.004)^t$, and for India $I(t)=1.19(1.0137)^t$. So, we need to solve the inequality

$$\begin{align} 1.19(1.0137)^t & > 1.34(1.004)^t\\ \left(\frac{1.19}{1.34}\right)\left(\frac{1.0137}{1.004}\right)^t &>1\\ \left(\frac{1.0137}{1.004}\right)^t & > \left(\frac{1.34}{1.19}\right)\\ t\log\left(\frac{1.0137}{1.004}\right)& > \log\left(\frac{1.34}{1.19}\right)\\ t & > {\log(1.34/1.19)\over\log(1.0137/1.004)}\\ t& > 12.35 \end{align}$$

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