How to find the circumference of a circle in pre-algebra - Math

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Question

An ant is standing at the center of a perfectly circular plate. If the ant crawled in a straight line, he would have to crawl 6 inches to reach the edge of the plate. How many inches would he crawl if he crawled a full circle around the edge of the plate?

Answer

We need to find the circumference:

$\text{circumference of a circle} = 2\pi r = d\pi$

In this formula stands for the radius and stands for the diameter.

The distance the ant must crawl to the edge from the center is the radius of the circle.

Plug in 6 inches for :

$\text{circumference of a circle} = 2\pi r = 2\pi6 = 12\pi$

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Question

If a circle has a radius of meters, what is its circumference?

Answer

The formula for the circumference of a circle is ${\pi}d$ , where is the diameter. This can also be written as $2{\pi}r$ , where is the radius of the circle. We were given the radius, so we take the second formula and plug in for .

$2{\pi}r = 2{\pi}(4) = 8{\pi}\ \textup{meters}=8\pi\ m$

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Question

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

Answer

Use the circumference formula $C=2\pi r$ and plug in 6 for . Leave $\pi$ in your answer to get $12\pi$ .

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Question

If the circumference of a circle is $8\pi$ , what is the radius of the circle?

Answer

The formula for the circumference of a circle is $C=2\pi r$ .

The problem gives us the circumference, so plug that in:

$8\pi=2\pi r$

Notice that the $\pi$ 's cancel out:

Divide both sides by :

$\frac{8}{2}=r$

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Question

What is the circumference of a circle with a radius of ?

Answer

To find the circumference of a circle given the radius we must first know the equation for the circumference of a circle which is

We then plug in the number for the radius into the equation yielding

$Cicumference=2(15)\pi$

We multiply to find the value for the circumference is $30\pi$ .

The answer is $30\pi$ .

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Question

What is the circumference of a circle with a radius of ?

Answer

To find the circumference of a circle given the radius we must first know the equation for the circumference of a circle which is

We then plug in the number for the radius into the equation yielding $C=2(\pi)(15)$

We multiply to find the value for the circumference is $30\pi$ .

The answer is $30\pi$ .

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Question

What is the circumference of a circle with a radius of ?

Answer

To find the circumference of a circle given the radius we must first know the equation for the circumference of a circle which is

We then plug in the number for the radius into the equation yielding

$C=2(35)(\pi)$

We multiply to find the value for the circumference is $70\pi$ .

The answer is $70\pi$ .

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Question

What is the circumference of a circle with radius ?

Answer

Remember, the formula for circumference of a circle is $C=2\pi r$ .

Plug in our given values:

$C=2\pi r$

$C=2\pi*3$

$C=6\pi$

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Question

If the circumference of a circle is $8\pi$ , what is the diameter of the circle?

Answer

The diameter of the circle is twice the radius, or . We first need to find the radius using the information that has been given to us.

The formula for the circumference of a circle is $C=2\pi r$ .

The problem gives us the circumference, so plug that in:

$8\pi=2\pi r$

Notice that the $\pi$ 's cancel out:

Divide both sides by :

$\frac{8}{2}=r$

Plug that into our first equation:

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Question

If the diameter of a circle is , what is the circumference?

Answer

The formula for circumference is $C=2\pi r$ . The problem gives us the diameter instead of the radius, so we need to convert.

The diameter is twice the radius or .

This means that, for this circle, .

Divide both sides by :

$\frac{14}{2}=r$

Plug this value into our initial equation to solve:

$C=2\pi r$

$C=2\pi *7$

$C=14\pi$

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Question

What is the circumference of a circle with a radius of ?

Answer

To find the circumference of a circle we must first know the equation for the circumference of a circle, which is $C=2\pi r$ .

We then plug in the given value for the radius, yielding $C=2(\pi)(31)$ .

We multiply to find the value for the circumference is $62\pi$ .

Thus answer is $62\pi$ .

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Question

What is the circumference of a circle with a radius of ?

Answer

The formula for circumference of a circle is $C=2\pi r$ .

Plug in our given information and solve.

$C=2\pi r$

$C=2\pi *5$

$C=10\pi$

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Question

What is the circumference of a circle with a radius of ?

Answer

The formula for circumference of a circle is $C=2\pi r$ .

Plug in our given values.

$C=2\pi6$

$C=12\pi$

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Question

What is the circumference of a circle with radius of ?

Answer

The formula for circumference of a circle is $C=2\pi r$ .

Plug in our given values.

$C=2\pi3$

$C=6\pi$

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Question

What is the circumference of a circle with a radius of ?

Answer

The formula for circumference of a circle is $C=2\pi r$ .

Plug in our given values.

$C=2\pi11$

$C=22\pi$

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Question

What is the circumference of a circle with a radius of ?

Answer

The formula for the circumference is $C=2\pi r$ .

Plug in our given radius and solve.

$C=2\pi r$

$C=2\pi 2.5$

$C=5\pi$

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Question

What is the circumference of a circle with a radius of ?

Answer

To find the circumference of a circle given the radius, we must first know the equation for the circumference of a circle which is

We then plug in for the radius into the equation yielding

$C=2(\pi)(16)$

We multiply to find the value for the circumference is

$C=32\pi$

The answer is $C=32\pi$ .

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Question

Find the circumference of a circle with a diameter of 4 meters.

Answer

The formula for circumference is:

$C = 2\pi r$ where is the radius of our circle

In this case, we were given the diameter of meters. Thus, we know that the radius is meters (since the diameter is twice the radius). Plugging this into the formula, we have:

$C = 2 \pi \cdot 2 = 4 \pi$ meters.

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Question

What is the circumference of a circle with a radius of ?

Answer

To find the circumference of a circle, use the equation:

$Circumference=2\pi\cdot Radius$

Substitute the given value for the radius into the equation:

$Circumference=2\pi\cdot13$

$Circumference=26\pi$

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Question

What is the circumference of a circle with a radius of ?

Answer

The formula for the circumference of a circle is $C=2\pi r$ .

Plug in our given values and solve.

$C=2\pi r$

$C=2\pi (5)$

$C=10\pi$

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