ACT Math : How to find circumference

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #581 : Geometry

What is the circumference of a circle with a radius of six ft? Leave your answer in terms of .

Possible Answers:

Correct answer:

Explanation:

To find the circumference given the radius, simply double the radius and mulitply by .

Thus:

 

Example Question #114 : Circles

A running track can be formed by adding a semicircle to each of the short ends of a rectangle of dimension .

If Tracy runs one lap around the track described above, how far has she run?

Possible Answers:

Correct answer:

Explanation:

The questions really asks us to find the perimeter of the track.This would be the two long sides of the rectangle plus the circumferences of each of the two semicircles.

Each long side of the triangle is .

Each semicircle has a circumference that is  because the whole circumference is

 thus the semicircle circumference would be half of that or,

 and .

Since the diameter of the semicircle is equal to the width of the rectangle, . That means each semicircle has a circumference of . Since we have two semicircles on the track, we can sum the two semicircle circumferences and the two long sides of the rectangle that comprise the track to get .

Example Question #581 : Geometry

Find the circumference of a circle with radius 6.

Possible Answers:

Correct answer:

Explanation:

To solve, simply use the formula for the circumference of a circle.

In this particular case the radius of 6 should be substituted into the following equation to solve for the circumference.

Thus,

Example Question #301 : Circles

Ashley has a square room in her apartment that measures 81 square feet. What is the circumference of the largest circular area rug that she can fit in the space?

Possible Answers:

Correct answer:

Explanation:

In order to solve this question, first calculate the length of each side of the room. 

The length of each side of the room is also equal to the length of the diameter of the largest circular rug that can fit in the room. Since , the circumference is simply

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