A pile of coal pile into a cone, the bottom circumference is 25.12 meters, the height is 1.2 meters? I calculated the answer, and students, but not the same

A pile of coal pile into a cone, the bottom circumference is 25.12 meters, the height is 1.2 meters? I calculated the answer, and students, but not the same

Radius = 25.12 △ 3.14 △ 2 = 4m
Bottom area = 4 & # 178; × 3.14 = 50.24m2
Volume = 50.24 × 1.2 × 1 / 3 = 20.096 M3

A cone-shaped compost pile has a bottom circumference of 12.56m and a height of 1.8m. If 20 cubic decimeters are applied to each hectare of land, how many hectares of land can these fertilizers supply

Bottom radius: 12.56 ÷ (2 × 3.14) = 2m,
Fertilizer volume:
V = 3.14 × 2 ^ 2 × 1.8 △ 3 = 7.536 cubic meters = 7536 cubic decimeters,
Fertilized land: 7536 △ 20 = 376.8 ha