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

If the circumference of a circle is 31.4 cm, what is its radius? (Use π ≈ 3.14)

1. 3 cm

2. 5 cm

3. 7 cm

4. 10 cm

The correct answer is: 5 cm

To find the radius of a circle given its circumference, you can use the formula for the circumference, which is \( C = 2\pi r \), where \( C \) is the circumference and \( r \) is the radius. In this case, the given circumference is 31.4 cm. Using the approximation of \( \pi \) as 3.14, you can rearrange the formula to solve for the radius: \[ r = \frac{C}{2\pi} \] Substituting the known values into the equation: \[ r = \frac{31.4}{2 \times 3.14} \] Calculating the denominator: \[ 2 \times 3.14 = 6.28 \] Now, dividing the circumference by this value: \[ r = \frac{31.4}{6.28} \approx 5 \] Thus, the radius of the circle is approximately 5 cm. This matches one of the choices provided, indicating that this value accurately reflects the relationship between the circumference and the radius as defined by the mathematical principles involved.