64 solid iron spheres of radius r are melted to form a sphere of radius R. Find R : r.

4 : 1

64 solid iron spheres of radius r are melted to form a sphere of radius R.

Volume of 64 solid iron spheres of radius r = 64* 4Πr³/3

Volume of solid sphere R = 4ΠR³/3

Also, 4ΠR³/3 = 64* 4Πr³/3

R³ = 16* 4r³

R³ = (4r)³

The correct answer is Option (4) → 4 : 1