If the ratio of the diameters of two spheres is 3: 5, then what is the ratio of their surface areas?

Let the diameter's of two sphere are d₁ and d₂, respectively.
∴ Ratio of their surface areas = 4πr₁²/4πr₂²
= (2r₁)²/(2r₂)² = d₁²/d₂²
= (d₁/d₂)² = (3/5)² = 9/25 = 9 : 25