What does percentages mean?

The percentage symbol (%) is a mathematical tool commonly used describing the magnitude of a quantity relative to another. The amount represents the 100%.

Despite the use of percentage is very widespread in everyday life (just think of how it is used in the discount the products sold), it is not so immediate comprehension as often thought: more of everything is easily be misinterpreted comparing percentages.

To be clear about the meaning of a number that expresses a percentage, you must first understand what the reference value. In fact, if you change the reference value, immediately changes the number percentage. Despite the passage is trivial, very often gets overlooked because of its simplicity, creating confusion.

When comparing the percentage increases or reductions in percentages it is always necessary to consider what the base Percentage Formula: not always, in fact, you can make valid considerations by adding or subtracting percentages.
The sums and subtractions of percentages can be meaningful only if the base is the same, otherwise you will get a result that makes no sense, for example: If I have a station with two tracks and then I add one, I have increased my 50% tracks, my reference value is 2 (the two tracks exist) and my rise is 1 (if two is my 100% 1, which is half of 2 will be 50%).

If then the same station (with three tracks) take a binary, I reduced the number of rails of 33.3%. In fact my reference value is 3, while my reduction was 1. As you can see the tracks eventually did not increase, but remained two as at the beginning, but if I get 50%-33.3% with percentage calculator, I had an increase of 16.6% tracks that doesn’t correspond to the truth.
There are, in fact, any special reasons why you should preferably make a report as a percentage, if not their greater understanding of people due to their common usage, especially for reports “under” the percent.

The percentage is used a lot especially in statistics, also because it linked to the idea of intuitive “as many a to find if I take 100 random  b” and then the concept of sample.
The mistake arose precisely from the fact that you are comparing two percentages that have a different basis. Because a percentage value may make sense you must always specify what the base against which it is calculated, and the percentage values very often are not cumulative or Insights on the percentage calculation because they represent magnitudes that refer to different basic amount.