This worksheet is about frustums of cones.

**Method**

20 | |

5 |

A solid cone has a diameter of 5 cm and a height of 20 cm.

The top half of the cone is cut off half way up to leave a frustum behind.

**(i)** the radius of the circle at the top of the frustrum (using proportion) is half the base radius, so here it is 1.25 cm

**(ii)** the volume of the original cone is 1/3 base area x height, using base radius of 2.5 cm

**(iii)** the volume of the cone removed is 1/3 base area x height, using base radius of 1.25 cm

**(iv)** the volume of the frustum is obtained by subtracting these two volumes.