SOLUTION: Two concentric circles have circumferences 30pi & 40pi. Find the area of the ring-shaped between them. What are my steps to solving this problem?

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Question 678210: Two concentric circles have circumferences 30pi & 40pi. Find the area of the ring-shaped between them.
What are my steps to solving this problem?
Answer by pmatei(79) About Me  (Show Source):
You can put this solution on YOUR website!
Step 1: Find the radius of each circle.
2%2Api%2Ar%5B1%5D+=+30%2Api
r%5B1%5D+=+15
2%2Api%2Ar%5B2%5D+=+40%2Api
r%5B2%5D+=+20
Step 2: Find the areas of the 2 circles.
A%5B1%5D+=+pi%2Ar%5B1%5D%5E2+=+225%2Api
A%5B2%5D+=+pi%2Ar%5B2%5D%5E2+=+400%2Api
Step 3: Subtract the smaller circle area from the bigger circle area.
A%5Bring%5D+=+A%5B2%5D+-+A%5B1%5D+=+175%2Api