The spherical ball of lead 3 cm in diameter is melted and recast into 3 spherical balls. The diameters of two of these are 1 1/2 cm and 2 cm respectively. The diameter of third ball is? Choose the correct choice from the following.
A) 2.8  B) 2.5  C) 2.2  D) 2.0  E) 2.1

Rationale: "4 / 3 π * 3 * 3 * 3 = 4 / 3 π [ ( 3 / 2 ) 3 + 23 + r 3 ] r = 1.25 d = 2.5 answer : b"
Answer: B