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In maths learning, every learners will come across the terms "percent" or "percentage".
Percentage is a ratio.
It is a ratio between two numbers.
The denominator is normally the total of an item.
The unit used is %.
The above may be common knowledge for anyone doing percent maths problems.
However, what is the presentation of the solution that is appropriate?
Let's us do an example.
Example:
Class A has 30 students. If 40% of them are girls, how many are boys?
Solution:
Number of boys in the class = 30 - 40%
Now, is this "30 - 40%" correct?
The idea may be there, but someting is amiss.
What is this "40%"?
Can we just write 40% as it is?
The answer is NO!
Percentage is a ratio of the total (the class size of 30).
We cannot simply write 40% if we want to know the actual number.
The correct way is to present the step or working as: (40/100) x 30 = 12 students
We cannot simply write : 30 - 40%.
The correct way has to be 30 - (40/100) x 30 = 30 - 12 = 28 students.
2 mistakes, in concept, were made:
1) Number cannot subtract a percentage. Their units are different.
2) Percentage is a ratio, an indication of the proportion of a piece to the total. It is a relative term, not an absolute number. Thus, an absolute number cannot operate with a relative term.
Understanding this concept of "percent" and "percentage" will be handy and avoid the unnecessary trouble and anxiety of doing maths.
Tips:
Thinks of a slice of cake when doing "Percent". It has meaning only when compared to the whole cake.
Remember: Maths Is Interesting! And it WILL be get more interesting.
:D
Wednesday, 26 August 2009
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