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Rates are used to compare two quantities and often involve a period
of time.
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
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