Question : The population of a city increases at a rate of 5% per year. If the present population of the city is 3,70,440, its population three years ago was:
Option 1: 30,000
Option 2: 2,80,000
Option 3: 3,60,000
Option 4: 3,20,000
Correct Answer: 3,20,000
Solution :
Let the population three years ago be $x$.
Here, rate $r$ = 5%
Time, $n$ = 3 years
Present population = $x(1+\frac{r}{100})^n$
⇒ $370440=x(1+\frac{5}{100})^3$
⇒ $370440=x(\frac{21}{20})^3$
⇒ $x=\frac{370440×20×20×20}{21×21×21}$
$\therefore x = 320000$
Hence, the correct answer is 3,20,000.
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