Answer: (1/3)πh(R² + Rr + r²).
- A πh(R+r)/2, a simplified average radius form
- B (1/3)πh(R² + Rr + r²)
- C πh(R² + r²), omitting the cross term
- D (2/3)πh(R+r)², an incorrectly squared form
Correct answer: B. (1/3)πh(R² + Rr + r²)
Explanation: Frustum volume = (1/3)πh(R² + Rr + r²). Derived by subtracting smaller cone from larger.
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