Question

If the radius of a circle incresed by 20℅then the corresponding increase in the area of circle is ?

Answer 1

Let the initial radius be r
Therefore, final radius be= r + 0.2r = 1.2r
So increase in area will be
$\pi \: r ^{2} ( {1.2}^{2} - {1}^{2} )$
$= \pi {r}^{2} (1.44 - 1) \\ = 0.44\pi {r}^{2}$
So in percentage increase of area.. The required answer will be,
$\frac{0.44\pi {r}^{2} }{\pi {r}^{2} } \times 100 \\ = 44\%.(ans)$