Year 8 Interactive Maths - Second Edition

Rates

Clearly, the speed of a train is measured by the distance covered per hour.  For example, if a train covers 200 km in 4 hours, then the average rate of speed is given by

Often, we write down how many of the first quantity corresponds to one of the second quantity.  E.g. 50 kilometres per hour.

It is convenient to write a rate using per or / to indicate for each.  So, 50 kilometres per 1 hour is written as 50 km/h.

Abbreviations used to express some common rates are:

• km/h for kilometres per hour
• m/s for metres per second
• $/L for dollars per litre
• $/m for dollars per metre
• L/min for litres per minute

Example 1

Write each of the following quantities as a rate:
a.  A cyclist covers 90 km in 3 hours.
b.  Chris earned $68 for 4 hours work.

Solution:

Note:

To simplify rates, multiply or divide both terms by the same number.

Key Terms

rate, speed