Question

The Nagar Palika of a certain city started campaign to kill stray dogs which numbered 1,250 in the city. As a result, the population of stray dogs started decreasing at the rate of $20\%$ per month. Calculate the number of stray dogs in the city three months after the campaign started.

Answer 1

$\Rightarrow$ Present population of the stray dongs $\left(P\right)=1250$

$\Rightarrow$ Rate of decrease in population every month $\left(R\right)=20\%$

$\Rightarrow$ Time $\left(t\right)=3moths$

$\therefore$ Population of stray dongs after $3$ months $=P{(1-\frac{R}{100})}^t$

$=1250{(1-\frac{20}{100})}^3$

$=1250{\left(\frac{5-1}{5}\right)}^3$

$=1250\times \frac{64}{125}$

$=640$

$\therefore$ The number of stray dogs in the city are $640$.