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.

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 speed of the bus: 20km/h, we can find out when we reach our destination.
    50 pages/h, we can find out how long it would take to finish reading the book.

  2. Kat Yong Jie is very smart and6/11/2011 12:32:00 PM

    The average download speed of my Mac: 80Kbps, we can find out how long it takes for the software to be downloaded

    The speed of light: 300,000km/sec or 1,080,000,000 km/h, we can find out how far is a certain celestial object in space by using light years.

  3. 15 pages/h : we can find how long it takes to finish taking down notes.
    5 shirts/min : we can find how long it takes to finish folding the laundry.

  4. 10litres/km: We can find out the distance the car can travel before it needs refueling.

    $5/hour: We can find out how much we have to pay for the carpark by using this

  5. for matter to turn to energy, the formula is mc square. which is matter=velocity square and the velocity is refering to the speed of light. therefore matter needs to be travelling at 90000km/s. we can find out what happened in the big bang in detail.

    the speed of a shuttle exiting the earth in can go up to 8km/s. We can find out how long it takes for the space shuttle to reach outer space/ exits the earth atmosphere.

  6. 100 pens/hour - there are 100 pens produced in an hour in the factory.

    $1 / hour - $1 dollar to play 1 hour of games in the cyber cafe.

  7. $10/ hour - Employer get paid $10 per hour

    2 words/ 1 sec - Find out approximately how long it would take to type an entire essay

  8. 50 pages/hour - 50 pages read in an hour

    80 letters/min - wriiting out 80 letters in a minute

  9. 20 levels/hour - a kid plays 20 levels of a certain game per hour

    30 clothes/hour - a typical housewife takes one hour to iron 30 clothes

  10. 1500 rounds per minute (RPM) - An MG42 fires 1200-1500 RPM.
    5 bottles per hour - An alcoholic would drink Vodka at the rate of 5 bottles per hour before he passes out.

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  12. 4 chapters/hour- I takes a person an hour to read 4 chapters in a book
    19 words per minute- It takes a minute for a kid to TYPE 19 words

  13. 1 pen an hour- a teacher would need one pen when marking papers for an hour
    2 cups of coffee - is the number of cups of coffee needed by an adult for a day

  14. A carpark charge $1.00 for every hour the car is parked.

    A car goes at a rate of 60 km/h on the road.

  15. Typing a letter / second - How fast I can type an SOS message before... ( Up to your imagination ).

    Beats/second - Find out the tempo of the rhythm / song.

  16. The maximum speed for a normal car is 240km/h

    Our heart normally beats at 60beats per second

  17. Daily expenditure-$20/day
    Revolutions per minute- 300rpm

  18. 20qn/h = 20 questions per hour
    $2/pen = $2 per pen