Rule of three calculator

The Rule of Three, often referred to as the simple rule of three or the basic proportionality rule, is a fundamental mathematical principle that describes how to determine a fourth value when three values are known, and they are in proportion. Essentially, if two quantities A and B are related in such a way that their ratio remains constant, and we have a third quantity C that is related in the same way to an unknown quantity X, then A:B = C:X. By cross-multiplying, we can find the value of X.

The origin of the Rule of Three is hard to pin down precisely, but it has ancient roots and was employed in various early civilizations, from the Egyptians to the Greeks. Historically, it was especially useful for merchants and tradespeople for calculations involving conversions, trade, and commerce. The rule became a standard part of arithmetic curricula in medieval European schools and was a central topic in many ancient arithmetic textbooks.

Its enduring utility arises from its ability to simplify complex proportional problems into straightforward multiplications and divisions, making it an indispensable tool in various fields, from business and economics to engineering and sciences. Even today, with the advent of modern technology and sophisticated computational methods, the Rule of Three remains a foundational concept taught in mathematics education worldwide.