Question

The population of a town in China increases by 20% every year. If its present population is 2,16,000, find:
(i) its population after 2 years,
(ii) its population 2 years ago.

Answer 1

Present population=216000

Increment rate =20% every year

(i) Population after n years = Present population ${(1+\frac{r}{100})}^n$
$\Rightarrow$ Population after 2 years $=216000{(1+\frac{20}{100})}^2$

$\Rightarrow 21600\times \frac{120}{100}\times \frac{120}{100}=311040$

(ii)Let the Population 2 year ago is x
Present population = Population n years ago ${(1+\frac{r}{100})}^n$
$\Rightarrow$ 216000 = $x{(1+\frac{20}{100})}^2$

$\Rightarrow x=\frac{21600\times 100\times 100}{120\times 120}$
$\Rightarrow x=1,50,000$