Question

$27$ spherical iron balls of radius $5cm$ each are melted and recasted into a big sphere. The radius of the big sphere is

• A. 3 cm
• B. 9 cm
• C. 15 cm
• D. 5 cm

Answer 1

The correct option is C

15 cm

Volumes of big iron ball is same as the sum of volumes of $27$ iron balls.

$\Rightarrow \frac{4}{3}\times \pi R^3=27\times (\frac{4}{3}\times \pi r^3)$

$\Rightarrow R^3=27r^3$

$\Rightarrow R=3r=3\times 5=15cm$