# 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).

## Practice questions

- 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*m*^{2}

**B.**18 π*m*^{2 }**C.**14.31*m*^{2}

**D.**28.26*m*^{2}

**E.**18.35*m*^{2}

## 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

*m*^{2}.