# Circles

Words of “Wiz-dom”-The key to circle problems is the radius. All other measurements (diameter, circumference, and area) rely on it. So if you are given the radius, you can calculate everything else. If you are given anything else, you can calculate the radius. Using the formulas at the beginning of a math section, do the following review problems.

Diameter (d) = 2 times Radius (r)
Circumference (c) =
πd = 2πr
Area=
πr2

O is the center of the circle. The radius is 3.

What is the diameter? Answer #1

What is the circumference? Answer #2

What is the area? Answer #3

Words of “Wiz-dom”-The other issue the test writer wants to test is whether you understand that there are 360 degrees in a circle. Of course, this leads to applying rules related to portions of the area of a circle and the arcs of a circumference based on the number of degrees where two radii intersect. The formula looks like the following:

Answer the following review questions.

Circle O has a radius of 8.

What is the diameter? Answer #4

What is the circumference? Answer #5

What is the area? Answer #6

What is the length of arc ABC? Answer #7

What is the area of the wedge OABC? Answer #8

Sample Questions

13.  If the diameter of the circle O is 8, what is the area of the shaded region?

(A)
(B)
(C)
(D)
(E)

Answer to Question #13

5.  In the diagram above, the area of the circle is π. What is the area of the square?

(A) 1
(B) 2
(C) 4
(D) 8
(E) 12

Answer to Question #5

12. A 16-inch (diameter) pizza is cut into 8 equal slices. What is the perimeter of the one slice that Ms. Townsend ate?

(A) 2π
(B) π + 8
(C) π + 16
(D) 2(π + 8)
(E) 16π

Answer to Question #12

4.  A 16-inch (diameter) pizza is cut into 8 equal slices. What is the sum of the angles at the center of the pizza for the three pieces that were eaten by The Wiz?

(A)  90
(B) 100
(C) 105
(D) 120
(E)  135

Answer to Question #4

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