The radius of spherical ball = 3 cm
Volume of spherical ball = 4/3πr^{3}
= 4/3π × 3 × 3 × 3
= 36π cm^{3}
∵ Volume of spherical ball = Total volume of three small spherical ball
∵ The radii of the ball are 1.5 cm and 2 cm
∴ Let the radius of third ball = r
∴ Volume of spherical ball = Total volume of three small spherical balls
36π = 4/3π × (3/2)^{3} + 4/3π × (2)^{3} + 4/3 πr^{3}
36π = 4/3π × 27/8 + 4/3π × 8 + 4/3πr^{3}
36π = 4/3π(27/8 + 8 + r^{3})
(36π × 3)/4π = 27/8 + 8 + r^{3}
27 = (27 + 64)/8 + r^{3}
27 = 91/8 + r^{3}
27 – 91/8 = r^{3}
(216 – 91)/8 = r^{3}
125/8 = r^{3}
r = 5/2 cm
The diameter of the third ball = 2r = 2 × 5/2
= 5 cm