What is the area and circumference of a circle with diameter 22 mm?
The area of a circle is pi times the radius squared, and the circumference is pi times the diameter. Pi is the irrational number equal to approximately 3.14. The radius is half the diameter because it is the distance from the edge of the circle to the center point of the circle. So the radius is 22/2=11 mm. The area is pi times r^2=3.14*(11 mm)^2=379.94 mm^2. The circumference is pi*d=3.14*22mm=69.08 mm.
