Diameter = 1.8m circumference = 3.14 *1.8 = 5.652m.

Diameter = 1.8/2=0.9m circumference =3. 14*0.9=2.826.

Diameter = 1.83=0.6m circumference = 3.14 * 0.6 =1.884m.

2.

s = 1.8 * 1.8-0.9 * 0.9×3. 14 = 0.6966 mm2。

s = 1.8 * 1.8-0.45 * 0.45×3. 14×4 = 0.6966 mm2。

s = 1.8 * 1.8-0.3 * 0.3×3. 14×9 = 0.6966 mm2。

After reducing the circle, the amount of scrap left by tinplate is the same.