What is the circumference of a circle with a diameter of 10? (Use π ≈ 3.14)

Circumference is π × diameter (C = πd), or equivalently 2πr. With a diameter of 10: C = 3.14 × 10 = 31.4. Be careful not to use the area formula (πr²); the area here would be 3.14 × 5² = 78.5, offered as a distractor. Since the diameter is given directly, C = πd is the fastest route. The circumference is 31.4. Remember that circumference uses the diameter (or 2× radius) to the first power, while area uses the radius squared.