California Assessment of Student Performance and Progress (CAASPP) Math Practice Exam

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

1. 31.4 cm²

2. 78.5 cm²

3. 100 cm²

4. 157 cm²

The correct answer is: 78.5 cm²

To find the area of a circle, the formula used is \( A = πr^2 \), where \( A \) is the area and \( r \) is the radius of the circle. The radius is half of the diameter. Given that the diameter of the circle is 10 cm, the radius can be calculated as follows: \[ r = \frac{diameter}{2} = \frac{10 \, \text{cm}}{2} = 5 \, \text{cm} \] Now substituting the radius into the area formula: \[ A = πr^2 = π(5 \, \text{cm})^2 = π(25 \, \text{cm}^2) \] Using the approximate value of \( π \) as 3.14: \[ A ≈ 3.14 \times 25 \, \text{cm}^2 = 78.5 \, \text{cm}^2 \] This calculation shows that the area of the circle is 78.5 cm², confirming that this is the correct answer. Understanding the relationship between diameter and radius is crucial, as it directly affects calculations involving the area