Hello darknightcat Originally Posted by

**darknightcat** Assuming that the dimensions on the diagram are in cm, the solid is a hollow cylinder of length 7 cm and internal and external radii 4 cm and 8 cm, respectively. Its cross-sectional area is therefore:

$\displaystyle \pi8^2 - \pi4^2$

$\displaystyle =48\pi$

and its volume is:

$\displaystyle 7\times 48\pi$

$\displaystyle \approx 1056 \text{ cm}^3$

The density is the mass divided by the volume. So its density is:

$\displaystyle \frac{1144}{1056}\approx1.08\text{ gm/cm}^3$

4.The __of a pyramid are the faces of the pyramid that are not the base.

The missing words are: 'lateral faces' or 'slant faces'

Grandad