SSAT Upper Level Math : How to find the circumference of a circle

Example Questions

Example Question #11 : How To Find The Circumference Of A Circle

central angle of a circle has a chord with length . Give the circumference of the circle.

Explanation:

The figure below shows , which matches this description, along with its chord :

By way of the Isosceles Triangle Theorem,  can be proved a 45-45-90 triangle with hypotenuse 40. By the 45-45-90 Theorem, its legs, both radii, have length that can be determined by dividing this by , so

This is the radius, so the circumference is

Example Question #12 : How To Find The Circumference Of A Circle

Give the circumference of a circle that circumscribes a  triangle whose shorter leg has length .

Explanation:

If a right triangle is inscribed inside a circle, then the arc intercepted by the right angle is a semicircle, making the hypotenuse of triangle a diameter.

The length of a hypotenuse of a 30-60-90 triangle is twice that of its short leg, so the hypotenuse of this triangle will be twice , or

.

This is the diameter, also, so the circumference is  times this, or .

Example Question #13 : How To Find The Circumference Of A Circle

Find the circumference of a circle with a diameter of 14.

Explanation:

Write the formula to find the circumference of a circle.

Substitute the diameter into the formula.

Example Question #14 : How To Find The Circumference Of A Circle

Find the circumference of the circle with an area of .

Explanation:

Write the formula for the area of the circle.  The radius is needed to find the circumference of the circle.

Substitute the area.

The radius of the circle is 3.  Substitute this in the circumference formula.

Example Question #15 : How To Find The Circumference Of A Circle

The track at Cesar Chavez High School is a perfect circle of radius 500 feet, and is shown in the above figure. Rafael starts at point C, runs around the track clockwise twice, and continues to run clockwise until he makes it to point D. Which of the following comes closest to the number of miles Rafael has run?

Explanation:

The circumference of a circle with radius 500 feet is

feet.

Rafael runs this distance twice, then he runs from Point C to D, which is about one-fifth of this distance. Therefore, Rafael's run will be about

feet.

Divide by 5,280 to convert to miles:

miles.

Of the given choices,  miles is the closest to the correct length.

Example Question #16 : How To Find The Circumference Of A Circle

The track at Eisenhower High School is shown above; it is comprised of a square and a semicircle.

Mike begins at Point A, runs five times around the track clockwise, and continues further until he reaches Point C. Which of the following comes closest to the distance Mike runs?

Explanation:

First, it is necessary to know the length of the semicircle connecting Points B and D, which has diameter 500 feet; this length is

feet.

The distance around the track is about

feet.

Mike runs around the track five times, which is a distance of about

feet.

He then proceeds to Point B, which is an additional 500 feet, and to Point C, which is half the semicircle, or

feet.

feet.

Divide by 5,280 to convert to miles:

miles.

Of the choices, the closest is  miles.

Example Question #17 : How To Find The Circumference Of A Circle

The track at Douglas MacArthur High School is shown above; it is the composite of a square and a semicircle.

Jennifer wants to run one mile. If she begins at Point A and begins running clockwise, where will she be when she is finished?

Between Point D and Point E

Between Point B and Point C

Between Point E and Point A

Between Point A and Point B

Between Point C and Point D

Between Point E and Point A

Explanation:

First, it is necessary to know the length of the semicircle connecting Points B and D, which has diameter 400 feet; this length is

feet.

The distance around the track is about

feet.

Divide this into 5,280 feet (one mile):

This means that Jennifer will run two times around the track to return to Point A. She will have 1,624 feet to go, so she will do the following:

She will run 400 feet from A to B, leaving  feet;

She will run 628 feet from B to D, leaving  feet;

She will run 400 feet from D to E, leaving  feet;

She will then run the remaining 196 feet from Point E toward Point A.

The correct response is that she will be between Point E and Point A.

Example Question #18 : How To Find The Circumference Of A Circle

The track at Madison High School is a perfect circle of radius 600 feet, and is shown in the above figure. Boris wants to run around the track for one mile. If Boris starts at point A and runs clockwise, which of the following is closest to the point at which he will stop running?

(Assume the five points are evenly spaced)

Explanation:

A circle of radius 600 feet will have a circumference of

feet.

Boris will run one mile, or 5,280 feet, which will be about

tiimes the circumference of the track, or, equivalently, once around the track, plus another two-fifths of the circle. This means he will end up closest to point C.

Example Question #19 : How To Find The Circumference Of A Circle

If you have a circular yard and need to put up a fence around the outside, you would use the formula  to figure out the amount of fence you need.

True

False

False

Explanation:

To figure out the amount of the fence around a circular yard, you need to find the circumference of the yard.  The equation for the circumference of a cirle is  and not .

Example Question #20 : How To Find The Circumference Of A Circle

Find the circumference of a circle with a diameter of 12.