The population of a city increases 15% annually. If the present population is 20,700, find the population a year ago.

Given,

The present population = 20700

Rate = 15%

Let the population of the previous year be x.

A number of years (n) = 1.

$20700=\mathrm{x}\times \left(1+\frac{15}{100}\right)$

$20700=\mathrm{x}\times \left(1+0.15\right)$

$\mathrm{x}=\frac{20700}{1.15}=18000$

Therefore, the population of a city a year ago was 18000.