Definitions:

From Wolfram MathWorld:

Decimal is the base-10 notational system for representing real numbers. The expression of a number using the decimal system is called its decimal expansion, examples of which include 1, 13, 2028, 12.1, and 3.14159.

Each of the Arabic numerals 0 to 9 is called a decimal digit, and the period placed to the right of the units place in a decimal number is called the decimal point (or, in the case that a comma is instead used for this purpose, the decimal comma).

Decimal -- from Wolfram MathWorld

A general example to help you recognize patterns and spot the information you're looking for

Addition $${ 12.35 + 5.287 = 17.637}$$ Subtraction $${12.993 - 2.28 = 10.713}$$ Multiplication $${2.3 * 4.5 = 10.35}$$ Division $${12.22 / 0.4 = 30.55}$$

Everyday. Currency uses the decimal system.

Converting Fractions to Decimals Example

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Length: 2:17

Decimals and Fractions

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Length: 2:42

Subtracting Mixed Numbers Word Problem

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Length: 4:41