Answer: 3/r.
- A 3/r
- B 4/r
- C r
- D 3r
Correct answer: A. 3/r
Explanation: S = 4πr², V = (4/3)πr³. S/V = 4πr² / (4πr³/3) = 3/r.
Three standard 3D solids and their key formulas: a cylinder's volume scales with the full height, a cone's volume is exactly one-third of the cylinder with the same base and height, and a sphere's volume and surface area both follow distinct r-based formulas worth memorising separately.
Concept context
Perimeters, areas, and volumes of 2D and 3D shapes