Practice Math Questions for Praxis: Area and Circumference of Circles
When you take the Praxis Core exam, it pays to have a well-rounded knowledge of circles—especially their area and circumference. In the following practice questions, you work both backwards (finding a circle’s radius given its circumference) and forward (finding a circle’s area given its radius).
- A circle has a circumference of 20π in.
What is the radius of the circle?
A. 4.5 in.
B. 15 in.
C. 10 in.
D. 20 in.
E. 17.5 in.
- The two circles have congruent radii. If the radius of one circle is 3 m, what is the area of the other circle, rounded to the nearest hundredth?
A. 6π m2
B. 18 π m2
C. 14.31 m2
D. 28.26 m2
E. 18.35 m2
Answers and explanations
- The correct answer is Choice (C).
The circumference of a circle is 2 times pi times the radius. You can use the formula for circumference, fill in what you know, and solve for r, the radius of the circle:
The radius of the circle is 10 in.
- The correct answer is Choice (D).
The circles’ radii are congruent, which means they have the same measure. Because one circle’s radius is 3 m, the circle in question has a radius of 3 m. You can use the formula for the area of a circle:
Because pi rounded to the nearest hundredth is 3.14, you can multiply 9 by 3.14:
9 × 3.14 = 28.26
The area of the circle, rounded to the nearest hundredth, is 28.26 m2.