A bucket is shaped like the frustum of a cone: its top radius is 20 cm, its bottom radius is 12 cm and its vertical height is 15 cm. How many litres of water does it hold? (Use π = 3.14, 1000 cubic cm = 1 litre, and give the answer correct to two decimal places.)

Question

Accepted Answer

12.31. For a frustum, volume = (πh/3)(R² + Rr + r²) = (3.14 x 15/3)(400 + 240 + 144) = 15.7 x 784 = 12308.8 cubic cm, which is 12.31 litres. The trap 8.54 omits the cross term Rr and uses only R² + r² = 544; 36.93 leaves out the 1/3; 12308.8 is the right volume left in cubic cm and never converted to litres.

A bucket is shaped like the frustum of a cone: its top radius is 20 cm, its bottom radius is 12 cm and its vertical height is 15 cm. How many litres of water does it hold? (Use π = 3.14, 1000 cubic cm = 1 litre, and give the answer correct to two decimal places.)

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