The population of a town was decreasing every year due to migration. The present population of the town is 6,31,680. Last year the migration was 4% and the year before last, it was 6%. What was the population 2 years ago?

Given,

P = 6,31,680

r₁ = 4%

r₂ = 6%

n = 1 year

By formula,

Population n years ago = $\dfrac{P}{\Big(1 - \dfrac{r$1}{100}\Big) \times \Big(1 - \dfrac{r2}{100}\Big)}

Substituting the values in formula,

$\text{Population 2 years ago}= \dfrac{631680}{\Big(1 - \dfrac{4}{100}\Big) \times \Big(1 - \dfrac{6}{100}\Big)} \\[1em] = \dfrac{631680}{\Big(\dfrac{100 - 4}{100}\Big) \times \Big(\dfrac{100 - 6}{100}\Big)} \\[1em] = \dfrac{631680}{\Big(\dfrac{96}{100}\Big) \times \Big(\dfrac{94}{100}\Big)} \\[1em] = \dfrac{631680 \times 100 \times 100}{96 \times 94} \\[1em] = \dfrac{6316800000}{9024} \\[1em] = 700000.$

Hence, the population of the town 2 years ago was 700000.