Inner Circle: about 28.27 feet Outer Circle: about 43.98 feet
Practice makes perfect
We want to determine the circumference of both circles. Let's start by looking at the given diagram!
Looking at the diagram, we can see that we have two concentric circles. We can recall that concentric circles have a common center and differ from each other by their radii.
We can also notice that our inner circle has a diameter of 9 feet. Now we can calculate the circumferences of the inner circle and the outer circle. We can do these things one at a time.
Inner Circle
First, we can recall the formula for the circumference of a circle.
C=π d textor C=2π r
Let's substitute 9 for the diameter d in the formula!
The inner circle has a circumference of 9π feet or about 28.27 feet.
Outer Circle
We want to calculate the circumference of the outer circle. We can begin by finding the radius of the outer circle on the given diagram.
Notice that the radius of the outer circle is the sum of the radius of the inner circle, 4.5 feet, and 2.5 feet.
4.5+ 2.5= 7
Let's substitute 7 for r in the formula for the circumference of the outer circle!
