## Wednesday, June 8, 2011

### June Vacation 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.

When we describe 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.

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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. We use rate to calculate the amt of water we used per month.
We use rate in MRT , as we need to count the time for next train to arrive so we use rate in the speed of the train

2. We use rate to describe the speed we are driving at. E.g. The car is moving at 60 kilometers per hour.
We use rate to describe the cost of houses. E.g. The house costs \$1500 per square meter.

3. We use rate to calculate our currency changes
We use rate to plan diets.

4. We use rate to calculate land.
We use rate to calculate water usage

5. We use rate to calculate how fast we must drive/walk in order not to be late for an appointment.
We use rate to calculate how much a house cost (\$700/m^2) so that the total amount would not go out of budget.

6. We use rate to calculate the price of a house
e.g.\$1234 per square foot(psf)
We use it to calculate driving speeds
e.g.123km/h

7. We use rate to calculate work pays.
e.g. \$1200 per month.
We use rate to calculate delivery at a post office.
e.g. \$1.50 for every 500g.

8. We can use rate to calculate how fast our heart is beating.
Example: 100 heartbeats per minute
We can use rate to calculate your driving speed to avoid speeding.
Example: 100 kilometers per hour

9. We can use rate for weather forecasting by measuring the speed of the wind (Km/h)

We can use rate for comparing firearms by comparing their rate of fire (RPS[rounds per second])

10. We can use rate to calculate the petrol consumption of a vehicle [km/litre]

We can use rate to calculate how many pages a printer prints in an amount of time. [pages/minute]

11. We can use rate to calculate the quality of gaming mice.(DPI=Dots Per Inch)
Example- the mouse has 2000DPI
We can use rate to calculate birth or death(population)
Example- the birth rate is 20000 babies per year

12. 1) We can use rate to describe the 'heart rate' of someone [beats/sec]
2) We can use rate to describe how fast something moves [km/h or m/s]

13. 1) we can use rate to measure the speed of a moving object. (km/h or m/s)
2) we can use rate to measure the number of pages read per unit hour. (# of pages read/h)

14. 1) We use it to calculate the cost of a piece of land. (\$1000 per m^2)
2) We use it to calculate the speed of a moving vehicle. (km/h)

15. We can use it to find out how fast we jog or run during our exercise. ( 100M/Minute )

We can use it to find out how many times we eat in a day. ( 3 meals/Day.. )

16. We can use rate to count the speed we are travelling at. (kilometer per hour)

We can use rate to count our salary. (\$12 per hour)

17. We can use it to measure, the current speed of the internet. (10Mb/s)

We can also use it to find the price of land. (\$200 psf)

18. We use it to measure the pressure (N/m)
we use it to measure the speed (m/s)

19. We use rate to measure speed(km/h or m/s). For example, a car is travelling at 80km/h.
We use rate to measure time as well. For example, how much a company charges you every hour when you rent a car.

20. We use rate to find out the speed in which we are driving
( Eg 80 km/h)

We use rate to calculate taxi fares
( Eg 20 cents / 100 m )