SSC CGL 4 Sep 2016 Paper

Slant height of cone (l)
= $\sqrt{{\mathit{r}}^2+{\mathit{h}}^2}$
= $\sqrt{{30}^2+{40}^2}$
= $\sqrt{900+1600}$
= $\sqrt{2500}$ = 50 cm
∴ Curved surface area of cone
= πrl
= (π × 30 × 50) sq. cm
= 1500 π sq. cm
If the radius of sphere be R cm, then
$4\mathit{\pi }{\mathit{R}}^2$ = 1500 π
⇒ ${\mathit{R}}^2$ = $\frac{1500}{4}$ = 375
⇒ R = $\sqrt{375}$ = $\sqrt{5\times 5\times 15}$
= 5 $\sqrt{15}$ cm