Circles: word problems
Ryan used a drafting compass to draw a circle on paper. The circle was 12 cm in radius. How many square centimeters were inside the circle?
Area = π × r^{2}
Area = π x 12^{2} = π x 144 = 144 π cm^{2}
π ≈ 3.14, so the area is 3.14x144=452.16 inches squared
Robert drew a circle that has a diameter of 16 inches. What is the area of his circle?
Area = π × r^{2}
You are told that the diameter is 16 inches, so the radius is onehalf of this measure, or 8 inches. Substituting the information into the area formula gives you
Area = π ×8^{2} = π × 64 = 64π
π ≈ 3.14, so the area is 3.14x64=200.96 inches squared.
Find the circumference of the following coin (Round to the nearest whole number):
1 Euro Coin


Diameter=23.25 mm 
C = π × d
Use 3.14 as an approximation for π.
C=(3.14)(23.25)≈73 mm.
Find the circumference of the following coin (Round to the nearest whole number):
Susan B.. Anthony Dollar


Radius=0.52 in 
C =2πr
Use 3.14 as an approximation for π.
C=(2)(3.14)(0.52)≈3.27 in.