PSAT Math : How to find the ratio of diameter and circumference

Example Questions

Example Question #11 : Diameter

Let  represent the area of a circle and  represent its circumference. Which of the following equations expresses  in terms of

Possible Answers:

Correct answer:

Explanation:

The formula for the area of a circle is , and the formula for circumference is . If we solve for C in terms of r, we get
.

We can then substitute this value of r into the formula for the area: