Madhya Pradesh Police Exam Model Paper 2

Given:
Radius of the circle is decreased by 10%.
Formula Used:
Are $=\mathit{A}=\mathit{\pi }{\left(\mathit{r}\right)}^2$
Calculation:
Let radius initially = r = 10 cm
⇒Area $=\mathit{A}=\mathit{\pi }{\left(\mathit{r}\right)}^2=10\mathit{\pi }\mathit{c}{\mathit{m}}^2$
⇒ New radius after 10% decrease $=\mathit{r}=10\times \frac{90}{100}=9\mathit{c}\mathit{m}$
⇒ New area $\mathit{A}\prime =\mathit{\pi }{\left(9\right)}^2=81\mathit{\pi }\mathit{c}{\mathit{m}}^2$
∴ % decrease in area $=\frac{100\mathit{\pi }-81\mathit{\pi }}{100\mathit{\pi }}\times 100=19$