3. 14×4×2×8=200.96 (square decimeter)

3. 14×4? =50.24 (square decimeter)

200.96+50.24 = 25 1.2 (square decimeter) =2.5 12 (square meter)

2.5 12×0.25≈0.63 (kg)

Answer: * * * needs 0.63kg of paint. (The number shall be kept to two decimal places. )

2.5 cm =0.5 decimeter

0.628×5=3. 14 (square decimeter)

0.628÷3. 14÷2=0. 1 (decimeter)

3. 14×0. 1? × 100=3. 14 (square decimeter)

3. 14+3. 14 = 6.28 (square decimeter)

A: It takes at least 6.28 square decimeters of iron to make 65,438+000 such cans.

3,6.28 ÷ 3.14 ÷ 2 =1(decimeter)

3. 14× 1? =3. 14 (square decimeter)

Answer: With two circles with an area of 3. 1.4 square decimeter, a cylinder with the largest surface area can be glued together.