When you say "Percent" you are actually saying "per 100" or /100 or % (see the 100 in the symbol?)

Written as an equation: B = P% * A

The 'what' is B that we want to solve.

First convert percentage to decimal, dividing it by 100,

then multiply that amount by A.

Written using the percentage formula: B = 15% * 35

First convert percentage to a decimal 15/100 = 0.15

The multiply 0.15 with the amount 35

B = 0.15 * 35 = 5.25

So 15% of 35 is 5.25

As for the history of percentages, the concept of using ratios to express proportions has been around for thousands of years, with examples of fractions and percentages appearing in ancient Egyptian and Babylonian texts. However, the modern concept of percentages as we know it today was popularized in Europe during the 17th and 18th centuries by mathematicians such as John Graunt, William Petty, and Pierre-Simon Laplace. These mathematicians used percentages to express statistical data, such as population growth rates and mortality rates, which helped to lay the foundation for modern statistical analysis. Today, percentages are used in a wide range of fields, from finance and economics to science and engineering, as a way to express proportions and compare different quantities.

John Maynard Keynes was a renowned British economist and mathematician who lived from 1883 to 1946. Keynes made significant contributions to the field of economics, particularly in the area of macroeconomics, and is widely regarded as one of the most influential economists of the 20th century.

One of Keynes' most significant contributions to economics was his use of percentages to help understand economic data. In his seminal work, "The General Theory of Employment, Interest and Money," Keynes used percentages to express changes in economic variables such as investment, consumption, and savings. By doing so, he was able to create a framework for understanding how changes in these variables could impact the overall economy.

For example, Keynes used the percentage formula to express the relationship between changes in investment and changes in income. He argued that an increase in investment would lead to a corresponding increase in income, and that this relationship could be expressed as a percentage. By calculating the percentage increase in income for a given increase in investment, Keynes was able to create a model for understanding the relationship between investment and economic growth.

Keynes' use of percentages was not limited to economic theory, however. He also used percentages to analyze economic data, such as changes in the unemployment rate and the growth of industrial production. By using percentages to express these changes, Keynes was able to create a framework for understanding how the economy was performing and what policy changes might be necessary to improve economic outcomes.

Keynes' legacy continues to influence economic thinking to this day, and his use of percentages remains an important tool for understanding economic data. Whether you are an economist, a business owner, or a casual observer of the economy, understanding the percentage formula and how it can be used to express changes in economic variables is essential for making informed decisions and understanding the world around us.