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prealgebra intermediate
Problem
Two circles have the same center (Circles which have the same center are called concentric.) The larger circle has radius and the smaller circle has radius Determine the area of the ring between these two circles. 
Solution
The area of a circle with radius is
So the area of the larger circle is and the area of the smaller circle is
The area of the ring between the two circles is the difference of these two areas.
Therefore, the area of the ring is
So the area of the larger circle is and the area of the smaller circle is
The area of the ring between the two circles is the difference of these two areas.
Therefore, the area of the ring is
Final answer
64\pi