Pre-Algebra : Circumference of a Circle

Study concepts, example questions & explanations for Pre-Algebra

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Example Questions

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Example Question #11 : Circumference Of A Circle

Find the circumference of the circle with a diameter of .

Possible Answers:

Correct answer:

Explanation:

Write the formula for the circumference of a circle.

Substitute the diameter.

Example Question #12 : Circumference Of A Circle

Find the circumference of a circle with an area of 5.

Possible Answers:

Correct answer:

Explanation:

Write the formula for the area of a circle.

Substitute the area to find the radius.

In order to solve the equation, we have to isolate the variable. We do this by performing the same operation to either side of the equation.

Write the formula to find the circumference of the circle.

Substitute the radius.

Example Question #13 : Circumference Of A Circle

If  find the circumference of a circle with a diameter of 10 inches.

Possible Answers:

Correct answer:

Explanation:

To solve, we will use the formula for circumference of a circle. The formula is

where . We know that the diameter of the circle is 10 inches. To find the radius, we simply divide by 2.

Therefore, 

We know , so we will substitute. We get

Therefore, the circumference of the circle is 31.4 inches.

Example Question #14 : Circumference Of A Circle

Find the circumference of a circle with a radius of 6cm.

Possible Answers:

Correct answer:

Explanation:

The formula to find the circumference of a circle is

where d is the diameter.  We know the radius is 6cm.  We also know to find the diameter, we take two times the radius.  Therefore, the diameter is 12cm.  So, substituting into the formula, we get

or

Therefore, the circumference of the cirlce is .

Example Question #15 : Circumference Of A Circle

A circle has a radius of . What is its circumference?

Possible Answers:

Not enough information given

Correct answer:

Explanation:

The formula for the circumference of a circle is 

.

So, we simply plug in the radius of  in order to solve for the circle's circumference:

Therefore, the circumference of ths circle is .

Example Question #16 : Circumference Of A Circle

What is the distance around a silo, if the distance from the center of the silo to the outside is ?

Possible Answers:

Correct answer:

Explanation:

What is the distance around a silo, if the distance from the center of the silo to the outside is ?

Picture a silo, its base is a circle. 

This problem want the circumference of that circle. It gives us the distance from the center to the outside of the circle, aka the radius.

Find circumference via the following formula:

So the distance is:

Example Question #17 : Circumference Of A Circle

Alfredo ran laps around his track. He had just learned in math about circumference and was wondering what the circumference of his circular track was. He knows that the diameter of his track is 100 feet. What is the circumference of Alfredo's track?

Possible Answers:

None of the above

Correct answer:

Explanation:

The only thing that needs to be known for this question is the equation for circumference which is:

 

Therefore your answer to this problem is simply

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