Q.In a village, the population increases annually by \(r\%\). If the population after \(n\) years is \(p\), then the population \(n\) years ago was – (a) \(p\left(1+\cfrac{r}{100}\right)^{-n}\) (b) \(p\left(1-\cfrac{r}{100}\right)^{-n}\) (c) \(p\left(1-\cfrac{r}{100}\right)^n\) (d) None of these
Answer: A
Let the population \(n\) years ago be \(x\).
∴ According to the condition, \(x(1+\cfrac{r}{100})^n = p\)
or, \(x = \cfrac{p}{(1+\cfrac{r}{100})^n}\)
or, \(x = p(1+\cfrac{r}{100})^{-n}\)
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