The radius of a sphere is 3 cm. Find, in terms of π, its volume.

Analyze the question: We need the volume of a sphere with radius r = 3 cm, written in terms of π.

Concept: The volume of a sphere is

V = (4/3)πr³

Solution:

1. Substitute r = 3: V = (4/3) × π × 3³
2. Compute the cube: 3³ = 27
3. Multiply: V = (4/3) × 27 × π V = 4 × 9 × π V = 36π cm³

Answer: The volume is 36π cm³, which is option D.

Check on the other options:

• B (108π) is what you get if you forget to divide by 3: 4 × 27 = 108.
• C (27π) is just r³ × π, which leaves out the 4/3.
• A (30π) doesn't come from the formula.

Exam tip: Do the division first. Since r³ = 27 is a multiple of 3, the 3 in the denominator cancels right away (27 ÷ 3 = 9), so you only need 4 × 9. Remember the formula as "four-thirds pi r cubed", and don't mix it up with the surface area, 4πr².