Percentage, according to the web-based Dictionary, is a mathematical number or ratio which is expressed as a portion of one hundred. It is derived from "per centum”, a Latin phrase which means "by the hundred.” The symbol "%” which also has a Latin origin is used to express the ratio.

Percentage is used widely to make important decisions. For students, it is difference between passing and failing an exam. Business persons use it to determine if their sales are growing or plummeting. Countries use it to determine winners of presidential elections. Governments use it to estimate and levy taxes on citizens’ salaries, and on imports and exports.

The earliest version of percentage calculation is said to have been during the Roman Empire. According to Wikipedia, an encyclopedia, Emperor Augustus would levy centesima rerum venalium which was a tax on goods at auction. The way the tax was calculated was similar to percentage in that fractions of one hundred were used.

However, Answers, a knowledge exchange platform, puts the use of percentage-like calculations at an earlier time, as early as 3500 BCE in India. The Chinese and Egyptians are also said to have made use of similar calculations.

During the Middle Ages (from 5th to 15th century), computations using 100 as the denominator started up again and by 17th century, they were commonplace. This is according to Reference, a knowledge resource.

Math Lab, a web-based mathematics resource, says that during the Middle Ages, which are also known as the Dark Ages, people were highly ignorant and therefore highly fearful and superstitious. People in power, such as priests, preyed on the fear to keep them ignorant about money and mathematics so that they could cheat them. They would, for instance, tell them that calculating or saying money out loud is evil.

Because of this, merchants were having a hard time pricing their goods. They were at a risk of being stoned or chased by people if they mentioned the cost of a product. The merchants came together and invented a story about percentage saying that God had told them in various dreams that if the word percentage or its subsequent symbol was used after a number, it would cast out evil of saying numbers. Therefore, instead of saying "this shirt is 120 cents,” they would say, "this shirt is 120 per cent.”

People are now more informed and keen on mathematics and the calculation of percentage remains an important part of decision making.

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