How to find the area of a circle in pre-algebra

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

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1

What is the area of circle with a radius of ?

$49\pi$

$7\pi$

$14\pi$

$70\pi$

Explanation

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

$Area=\pi(radius^{2})$

Substitute the given value for radius:

$Area=\pi(7^{2})$

$Area=49\pi$

2

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

$A=144\pi$

$A=12\pi$

$A=24\pi$

$A=188\pi$

Explanation

To find the area of a circle you must plug the radius into in the following equation

In this case the radius is so we plug it into to get

$A=12^{2}\pi$

We then multiply it by to get our answer

$A=144\pi$ .

3

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

$A=16\pi$

$A=12\pi$

$A=4\pi$

$A=8\pi$

Explanation

To find the area of a circle, you must plug the radius in for in the following equation:

In this case the radius is , so we plug in for to get $A=\pi(4^{2})$ .

$A=16\pi$

4

The area of a circle is $49 \pi$ . What is its radius?

Explanation

Here, we are given the area of a circle and asked to solve for the radius. We know that the formula for the area of a circle is $A = \pi(r)^{2}$

Plugging in the area, we can cancel out the pi on each side of the equation, so that

$r^{2} = 49$

Taking the square root, we find that

5

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

$A=7\pi$

$A=14\pi$

$A=42\pi$

Explanation

To find the area of a circle you must plug the radius into in the following equation

In this case the radius is so we plug it into to get

We then multiply it by to get our answer .

6

What is the diameter of a circle with an area of $169\pi$ ?

$13\pi$

$26\pi$

Explanation

The formula for the area of a circle is $A=\pi r^2$ .

Plug in our given values.

$A=\pi r^2$

$169\pi=\pi r^2$

Notice that the pi cancels out.

$\sqrt{169}=\sqrt{r^2}$

The diameter is twice the radius or .

For this circle that means that .

7

What is the area of a circle with radius of ?

$9\pi$

$6\pi$

$3\pi$

$27\pi$

$2\pi$

Explanation

The formula for the area of a circle is $A=\pi r^2$ .

Plug in our given values:

$A=\pi r^2$

$A=\pi*3^2$

$A=9\pi$

8

Find the area of a circle with a circumference of $26\pi$ .

$169\pi$

$13\pi$

$26\pi$

$52\pi$

Explanation

The circumference equation is $C = 2\pi r$

If we plug $26\pi$ into the equation, we can solve for the radius, which is .

Now, we look for the area of the circle based on the equation $A = \pi r^{2}$

$A = 169\pi$

9

If the diameter of a circle is , what is the area of that circle?

$121\pi$

$484\pi$

$66\pi$

$22\pi$

$11\pi$

Explanation

The area of a circle is $A=\pi r^2$ , but the problem gives us the diameter and not the radius.

The diameter is twice the radius, so . We can plug in our given values to find the radius:

$\frac{22}{2}=r$

Now we can plug this value into our equation for area:

$A=\pi r^2$

$A=\pi*11^2$

$A=\pi *121$

$A=121\pi$

10

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

$36\pi$

$12\pi$

$6\pi$

$36\pi^2$

$\frac{1}{6}\pi$

Explanation

The formula for area of a circle is $A=\pi r^2$ .

Plug in our given information:

$A=\pi 6^2$

$A=36\pi$

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