Thanks Prof Debi for the answer and Eddie for your question, I didn't realise till now that these two words can give different meanings even though they point to the same value.
In mathematics, a percentage is a number or ratio expressed as a fraction of 100. It is often denoted using the percent sign, "%", or the abbreviation "pct."
For example, 45% (read as "forty-five percent") is equal to 45/100, or 0.45. A related system which expresses a number as a fraction of 1,000 uses the terms "per mil" and "millage". Percentages are used to express how large or small one quantity is relative to another quantity. The first quantity usually represents a part of, or a change in, the second quantity. For example, an increase of $ 0.15 on a price of $ 2.50 is an increase by a fraction of 0.15/2.50 = 0.06. Expressed as a percentage, this is therefore a 6% increase.
Percentages are usually used to express values between zero and one. However, it is possible to express any ratio as a percentage; for example, 111% is 1.11 and −35% is −0.35.
As per usage, Percent in Singular groups direct(example. 10 percent, 20 percent, ...etc.,), Percentage is plural and generalizations indirect use ( The percentage of Gents who were loyal to .... etc.,)
I disagree with you. Percentage it is nor the plural of percent!
Percent vs Percentage. Always write out the number and the word percent at the beginning of a sentence (eg, "Ten percent..."). The noun percentage requires an adjective to describe its size (eg, "a large percentage") when it does not refer to specific numbers in the sentence.
"The word percent (or the symbol %) accompanies a specific number, whereas the more general word percentage is used without a number." This is quoted from the link provided by Costas. Thank you dear Costas.
In scientific writing when reporting results it is usually percent. When reporting a description of the results (discussion) it can be percentage. I think this definition sums it up:
But see Prof. Charles Darling's online Guide to Grammar and Writing