The population of a city is 320000. If the annual birth rate is 9.2% and the annual death rate is 1.7%, calculate the population of the town after 3 years.

Net growth rate = 9.2% - 1.7% = 7.5%.

By growth formula,

V = $V_0\Big(1 + \dfrac{r}{100}\Big)^n$

Putting values in formula we get,

$V = 320000\Big(1 + \dfrac{7.5}{100}\Big)^3 \\[1em] = 320000 \times \Big(\dfrac{107.5}{100}\Big)^3 \\[1em] = 320000 \times \Big(\dfrac{1075}{1000}\Big)^3 \\[1em] = 320000 \times \Big(\dfrac{43}{40}\Big)^3 \\[1em] = 320000 \times \dfrac{43}{40} \times \dfrac{43}{40} \times \dfrac{43}{40} \\[1em] \\[1em] = 320000 \times \dfrac{79507}{64000} \\[1em] = 5 \times 79507 \\[1em] = 397535.$

Hence, the population of the town after 3 years = 397535.