半径2×4÷3.14÷2=4/3.14米720×(3.14×4/3.14×4/3.14×1/4×1×1/3)=720×4/9.42≈305.7千克
poiuytr5556 ,你好:3.14÷(2÷1/4÷3.14÷2)²×1×1/3×720≈464(千克)