A ring with an outer diameter of 4 decimeters and an inner radius of 1 decimeter. The area of the ring is______ Square decimeter

4 △ 2 = 2 (decimeter), 3.14 × (22-12), = 3.14 × (4-1), = 3.14 × 3, = 9.42 (square decimeter); answer: the area of this ring is 9.42 square decimeter. So the answer is: 9.42

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