Math problem: Make 20 identical cylindrical ventilation pipes. The bottom of the ventilation pipe is 20cm in diameter and 1.2m in length. How many iron sheets are needed to make these ventilation pipes? Hello: The ventilation duct only needs to calculate the side area of the cylinder.

1.2m = 120cm

Section 1 required iron sheet area = 3.14× 20×120 = 7536 (square centimeter).

The area of iron sheet needed for 20 sections =7536×20= 150720 (square centimeter) = 15.072 (square meter).