Chap 9.2 RATE (L1) Rate in Everyday Situation

What's defined in Wikipedia: Rate (mathematics)
In mathematics, a rate is a ratio between two measurements, often with different units.[1]. If the unit or quantity in respect of which something is changing is not specified, usually the rate is per unit time. However, a rate of change can be specified per unit time, or per unit of length or mass or another quantity. The most common type of rate is "per unit time", such as speed, heart rate and flux. Rates that have a non-time denominator include exchange rates, literacy rates and electric flux.

In describing the units of a rate, the word "per" is used to separate the units of the two measurements used to calculate the rate (for example a heart rate is expressed "beats per minute"). A rate defined using two numbers of the same units (such as tax rates) or counts (such as literacy rate) will result in a dimensionless quantity, which can be expressed as a percentage (for example, the global literacy rate in 1998 was 80%) or fraction or as a multiple.

Rate is commonly used in our daily life. Here are some examples:
  • 40 km/h - 40 kilometres per hour
  • 30 steps/min - 30 steps in per minute
  • 2 l/hour - 2 litres per hour
  • 67 words/min - 60 words per 1 min
  • 80 m/week - 80 metres per week  
  • 25km/l - 25 kilometres per 1 litre
  • $90/m³ - $90 per cubic metre
Think of 2 real life situations in which we use the concept of rate to describe useful information.
Here is an example:
The Singapore Flyer rotates at the rate of 0.24 m/s or 0.76 km/h


  1. The driving limit in Singapore is 60km/h

    The frequency of MRT trains at peak hours is about 1 train per 3minutes

    1 train/3min

  2. The escalator moves at a rate of 1km/h.

    The driving limit in expressways are 90km/h.


  3. The baseballer threw the ball and it moved at a speed of 130km/h.

    Rate : 130km/h

    The chef prepared 50 dishes in an hour.

    Rate : 5 dishes/6 min

  4. The frequency of the traffic light turing green is 20 seconds.

  5. @Ziying:
    Instead of expressing 1 train for every 3 minutes, how about describing by the number of trains in an hour?

    @Jing Jie:
    How would you describe the speed of the escalator in a minute?

    It's quite difficult to imagine a ball remains in the air for an hour. How would you describe the speed of the ball in terms of metres/second or metres/minute?

    What would you get if you were to describe the number of times the traffic light turns green in a minute?