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The sixth grade math homework is urgent! ! How many cubic meters of steel is needed to manufacture the steel pipe under construction?
Idea: first calculate the annular area of the cross section (that is, the bottom of the steel pipe), and then multiply it by the length of 2 meters.
Solution: 30cm = 0.3m and 20cm = 0.2m.
The outer diameter of the annular section is 0.3 ÷ 2 = 0. 15m, and the inner diameter is 0.2 ÷ 2 = 0.1m.
The required steel for this steel pipe is: 3.14× (0.15× 0.15-0.1)× 2 = 0.0785 (cubic meter).