### Why do this problem ?

Use of units is a critical skill in the sciences, and one which
often leads to confusion.

This
problem will encourage students to understand the relationships
between various types of units, as well as possibly introducing
them to new important scientific units. It will also help to embed
the important skill of checking numerical answers to see if they
make sense in terms of orders of magnitude, along with a sense of
where units are of relevance in science.

### Possible approach

This question works well through discussion in pairs. Remind
the students that common sense works well when dealing with units:
for example, a cubic mm is clearly far smaller than the volume of a
bathtub.

### Key questions

What suggestions for units are possible in each case?

### Possible extension

Continue the question for other, more exotic units of measure (such
as those given in

New
units for Old )

### Possible support

Remind students the formulae for the compound measures, such
as volume.

Students might also struggle with the reasonably open nature
of the question. Remind them that there is no 'correct' answer and
common sense approximations will help.