25/3 14
2. In order to make a cylindrical barrel with a bottom diameter of 20 cm and a height of 40 cm, the wasted material is exactly 8% of the actual material of the barrel. How many pieces of iron do you need to make such a bucket?
3.14 * 20 * 40+3.14 *10 *10 = 2826 (square centimeter)
2826*( 1+8%)=3052.08 (square centimeter)
3. Cut a square with a diamond length of 8 cm into the largest cylinder. What is the surface area of this cylinder?
3.14 * 4 * 8+3.14 * 4 * 2 = 200.96 (square centimeter)
4. A cylindrical iron drum with no cover, 6.28 meters high, is just a square when it is unfolded sideways. How many square meters of materials does it take to make this bucket? What is the volume of this bucket?
Transverse area: 6.28*6.28=39.4384
Radius: 6.28/3. 14/2= 1
Bottom area: 3.14 *1*1= 3.14.
Materials used: 3. 14+39.4384=42.5784 (square decimeter) =0.425784 (square meter).
Volume: 3.14 *1*1* 6.28 =19.7192 (length)
5. Cut a cube with a rhombic length of 20cm into the largest cylinder. What is the volume of the cutting block?
20 * 20 * 20-3.14 *10 *10 * 20 =1720 (cubic centimeter)