10 Reading data from tables
Tables provide a neat and concise way of displaying information. Table 10.1 illustrates various important features, common to all tables of this type:
- a title
- a heading at the top of each column
- the ‘volume’ heading includes the units (litres in this case), so the unit does not have to be repeated after each number.
Note the way in which the volume heading and its units have been quoted as ‘Volume/litres’.
It is conventional always to use ‘quantity divided by units’ (usually in the form ‘quantity/units’) in labelling the headings of tables and the axes of graphs.
| Use of water | Volume/litres |
|---|---|
| Domestic – mains water supply | |
| flushing lavatory | 44 |
| bath and shower | 23 |
| washing machine | 16 |
| dishwasher | 1 |
| outside use (garden, car washing) | 4 |
| miscellaneous (drinking, cooking, cleaning) | 48 |
| Non-domestic – mains water supply | |
| commercial and industrial use | 189 |
| Non-domestic – rivers and underground supplies | |
| agriculture | 7 |
| electricity generation | 220 |
| industry | 52 |
When reading a value from the table, for example the estimated amount of water used in washing machines, the units from the heading must be re-attached to the appropriate number. In the case of the example, the units of litres must be given alongside the number 16; 16 litres of water are used in washing machines per person per day in the UK.
The way in which the table heading is given as ‘volume/litres’ is a reminder of the fact that the value (16 litres) has been divided by litres. The litres then cancel to give a pure number in the table:
Question 10.1
To practise reading the information presented in Table 10.1, answer the following questions:
- a.How much water does the average person in the UK use each day in the home for flushing the lavatory?
The number given in the second column of Table 10.1 on the same line as ‘flushing lavatory’ is 44, and we attach the units ‘litres’ to this. So the average person uses 44 litres of water per day for this purpose.
- b.What does the number 7 in the third row from the bottom of the table mean?
The entry in the third row from the bottom of the first column of the table is ‘agriculture’, so the number 7, together with the table title and the column heading, tells us that the use of water for agriculture in the UK is equivalent to 7 litres per day for each person in the country.
Now look at Table 10.2. The ‘Mass’ heading includes not just a unit but a power of ten too. This has been done to avoid giving a power of ten alongside each value and thus to make the table less cluttered; it also makes it easier to compare the different masses. Not only has the mass of each planet been divided by kg, it has also been divided by 1020, and both the units and the power of ten need to be re-attached when data are extracted from the table. Thus the mass of Mercury is 3 302 1020 kg, which is 3.302 1023 kg in scientific notation (since the decimal point has to be moved a further three places).
| Major planet | Mass/1020 kg |
|---|---|
| Mercury | 3 302 |
| Venus | 48 690 |
| Earth | 59 740 |
| Mars | 6 419 |
| Jupiter | 18 990 000 |
| Saturn | 5 685 000 |
| Uranus | 866 200 |
| Neptune | 1 028 000 |
Question 10.2
Use Table 10.2 to find the mass of the planet Uranus.
Remembering to incorporate the ‘1020 kg’ from the column heading, the mass of Uranus is 866 200 1020 kg. In scientific notation, this is 8.662 1025 kg to four significant figures (since the decimal point needs to be moved an additional five places).