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A rate is used to compare two quantities, which need not be
measured in the same units. The rate (or speed) is used to
describe how a quantity changes over a certain interval of time.
For example, the speed of a train is described as the distance
travelled (km) per hour.
We usually write a rate using per or /
to indicate that a quantity changes for each unit of
time.
For example, the speed of a train is 60 km per hour or 60 km/h.
Some common rates are:
- water rate per quarter
- council rate per quarter
- currency exchange rate
- telephone rental rate
- telephone charge per call
Abbreviations used to describe common rates include:
- L/km means litres per kilometre
- cm/s means centimetres per second
- m/min means metres per minute
- L/min means litres per minute
- ¢/min means cents per minute
- ¢/L means cents per litre
Example 5
Find the speed of a walker if he walks 24 kilometres in 3 hours.
Solution:
So, the speed of the walker is 8 km/h.
Example 6
Find the telephone call charge rate if a telecommunications company charges $1.80 for 12 calls.
Solution:
So, the rate is 15¢/call.
Example 7
Find the rate of reading if a student read 432 pages of a book in 16 days.
Solution:
So, the rate of reading is 27 pages/day.
Example 8
Solution:
Key Terms
rate, speed
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