# GED Math : Circles

## Example Questions

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### Example Question #1 : Radius And Diameter

What is the radius of a circle with a diameter of 12 inches?     Explanation:

The radius is half of the diameter: From here we plug in our diameter measure of 12 and solve for the radius:   ### Example Question #2 : Circles

What is the diameter of a circle with radius of 10 inches?     Explanation:

The diameter is twice the radius:  ### Example Question #1 : 2 Dimensional Geometry

What is the radius of a circle that has a circumference of ?

18

20

12

4

18

Explanation:

The equation for circumference of a circle is as follows: Plug in the given values and solve for the radius: Now we divide each side by : ### Example Question #1 : Circles

Find the diameter of a circle that has a circumference of ?

20

12.5

10

25

25

Explanation:

We know the equation for the circumference of a circle is . We also know that the the diameter is the twice the radius, so we can write .

Plug in the given values and solve:  ### Example Question #1 : Radius And Diameter

What is the diameter of a circle with a radius of 9?

16

20

18

6

18

Explanation:

The diameter of a circle is twice the radius:   ### Example Question #1 : Radius And Diameter

What is the radius of a circle given the diameter is 22?

11

9

6

15

11

Explanation:

The radius is half of the diameter, or 11.

### Example Question #7 : Circles

What is the diameter of a circle with an area of ?      Explanation:

In order to solve this question, start by finding the radius.  Recall that the area of a circle is computed as: For our data, this is: Solving for , we get: or Now, recall that the diameter is double the radius.  Thus, it is .

### Example Question #8 : Circles

What is the radius of a circle with a circumference of ?    Cannot be computed from the information provided Explanation:

Recall that the circumference formula is: Now, for your data, this gives you: You need to be careful, for some students get confused when they have to divide by .  However, just treat it like any other number or variable.  This means that you can solve for and get: ### Example Question #9 : Circles

What is the diameter of a circle given the area of 30?      Explanation:

Write the area formula of a circle. Substitute the area. Divide by pi on both sides.  Square root both sides.  The radius is: The diameter is double the radius.

The answer is: ### Example Question #1 : Radius And Diameter

What is the diameter of a circle if the area is ?      Explanation:

Write the formula for the area of a circle. Substitute the area into the equation. Divide by pi on both sides.   The diameter is twice the radius.

The answer is: ← Previous 1 3 4 5 6 7 8 9 17 18

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