விழுக்காடு

விழுக்காடு(இலங்கை வழக்கு:சதவீதம்) என்பது ஒரு விகிதம் அல்லது பின்னத்தை, முழு எண்ணாக வெளிப்படுத்த ஒரு வழியாகும். 100ஐ பகுவெண்ணாகக் (பின்னக்கீழ் எண்) கொண்டு இவ்வாறு செய்யப்படுகிறது. "45%" என்பது போன்ற ஒரு குறியீடு ("45 விழுக்காடு") 45/100 அல்லது 0.45 என்பதின் சுருக்கமாகும்.

எடுத்துக்காட்டாக,

"45 விழுக்காடு மனிதர்கள்..."

என்பது பின்வரும் இரண்டு சொற்றொடர்களுக்கும் சமமாகும்:

"ஒவ்வொரு 100 பேரிலும் உள்ள 45 பேர்..."

"மனித மக்கட் தொகையில் 0.45 பகுதி "

ஆக "இரண்டு விழுக்காடு" என்பதை,( % சின்னத்தால் குறிக்கப்படுவது), 2/100, அல்லது 0.02 என்ற எண்களாக கருதுவது எளிமையாகும்.

ஒரு விழுக்காடு 100ஐக் காட்டிலும் பெரிய எண்ணாகவும் இருக்கலாம். எடுத்துக்காட்டாக, 200 % என்பது ஒரு எண்ணை விட இரு மடங்கு கூடுதலான எண்ணை குறிக்கும். 100 விழுக்காட்டு உயர்வு இரு மடங்கு கூடுதலான எண்ணையும், 200 விழுக்காட்டு உயர்வு மூன்று மடங்கு கூடுதலான எண்ணையும் தரும். இதன் மூலம் விழுக்காட்டு உயர்வுக்கும் மடங்கு உயர்வுக்கும் உள்ள தொடர்பை அறியலாம்.

Confusion from the use of percentages

Many confusions arise from the use of percentages, due to inconsistent usage or misunderstanding of basic arithmetic.

Changes

Due to inconsistent usage, it is not always clear from the context what a percentage is relative to. When speaking of a "10% rise" or a "10% fall" in a quantity, the usual interpretation is that this is relative to the initial value of that quantity; for example, a 10% increase on an item initially priced at $200 is $20, giving a new price of $220; to many people, any other usage is incorrect.

In the case of interest rates, however, it is a common practice to use the percent change differently: suppose that an initial interest rate is given as a percentage like 10%. Suppose the interest rate rises to 15%. This could be described as a 50% increase, measuring the increase relative to the initial value of the interest rate. However, many people say in practice "The interest rate has risen by 5%". To counter this confusion, the unit "percentage points" is sometimes used when referring to differences of percentages. So, in the previous example, "The interest rate has increased by 5 percentage points" would be an unambiguous expression that the rate is now 15%. Often also, the term "basis points" is used, one basis point being one one hundredth of a percentage point. Thus, the interest rate above increased by 500 basis points.

Cancellations

A common error when using percentages is to imagine that a percentage increase is cancelled out when followed by the same percentage decrease. A 50% increase from 100 is 100 + 50, or 150. A 50% reduction from 150 is 150 - 75, or 75. The end result is smaller than the 100 we started out with.

In general, the net effect is:

(1 + x)(1 - x) = 1 - x²

i.e. a net decrease proportional to the square of the percentage change.

Owners of dot com stocks came to understand that even if a stock has sunk 99%, it can nevertheless still sink another 99%. Also, if a stock rises by a large percentage, you're still broke if the stock subsequently drops 100% meaning it has a zero value.

An example problem

Whenever we talk about a percentage, it is important to specify what it is relative to, i.e. what the total is that corresponds to 100%. The following problem illustrates this point.

In a certain college 60% of all students are female, and 10% of all students are computer science majors. Among the females, only 5% are computer science majors. What percentage of computer science majors are female?

We are asked to compute the ratio of female computer science majors to all computer science majors. We know that 60% of all students are female, and among these 5% are computer science majors, so we conclude that .6×.05 = .03 or 3% of all students are female computer science majors. Dividing this by the 10% of all students that are computer science majors, we arrive at the answer: 3%/10% = .3 or 30% of all computer science majors are female.

Word and symbol

In British English, percent is usually written as two words (per cent). In American English, percent is the most common variant. In the early part of the twentieth century, there was a dotted abbreviation form per cent., which came from the original Latin per centum. The concept of considering values as parts of a hundred is originally Greek.

The symbol for percent "%" evolved from a symbol similar except for a horizontal line instead of diagonal (c. 1650), which in turn evolved from an abbreviation of "P cento" (c. 1425). Traditionally, the symbol follows the number to which it applies.

In Unicode, there is also an "ARABIC PERCENT SIGN" (U+066A), which has the circles replaced by square dots set on edge.

In computing, the percent character is also used for the mod operation in programming languages that derive their syntax from C. The ASCII code for the percent character is 37, or 0x25 in hexadecimal. In the textual representation of URLs, a % immediately followed by a hexadecimal number denotes the ASCII code of a character that cannot be otherwise represented. Names for the percent sign include percent sign; mod; grapes in ITU-T, and the humorous double-oh-seven in INTERCAL.

தொடர்புடைய அலகுகள்

Percentage point.
Per mille (‰) 1 part in 1,000.
Basis point (relates to per ten thousand as percentage point to percent).
Parts per million (ppm).
Parts per billion (ppb).
Parts per trillion (ppt).
Baker percentage

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