Decimal number
Content
What are decimal numbers?
Decimal numbers are the values that represent numbers smaller than the unit, each decimal number has an integer and a decimal part, where the whole part is to the left of the decimal point and the decimal part to the right.
A decimal number is an approximate value that allows you to represent a rational and irrational number at an approximate value.
Learn more about: “Rational numbers”. →
Note: Depending on the author the decimal point is represented by a point (18.18) or represented by a comma (18,18), to avoid confusion it is preferable to use the point.
Which they are the decimal numbers?
Depending on the result we can classify the decimal numbers in different ways:

Exact decimal numbers: They are those that have a number of specific decimal numbers or in other words have a final number in the decimal part, for example:
0.5
12.5843
138.54 
Periodic Decimal Numbers: They are those that have an unlimited or infinite number of decimal cider and the decimal part has a certain pattern or period. Periodic decimal numbers in turn are classified as pure and mixed:
 Pure periodic decimal numbers: There is a period or pattern from the first decimal place, for example:
3.555555... Periodic = 5
13.181818... Periodic = 18
154.123123... Periodic = 123 Mixed periodic decimal numbers: The first decimal figures do not present a pattern or period but after some figures it begins to show a period, for example:
23.622222... Periodic = 2
5.135838383... Periodic = 83
245.01203010101... Periodic = 01  Decimal numbers not periodic: They are decimal numbers of infinite numbers but do not have a defined pattern, corresponds to irrational numbers, such as the number pi, square root of 2, etc.
Learn more about: “Irrational numbers”. →
Identify the amount it represents
Ones units (A), tens (B), hundreds (C) and thousand units (D) are aligned to the left of the point; to the right of the point the tenths (E), hundredths (F) and thousandths (G) are aligned.
We have as a result: 1 thousand units, 3 hundreds, 5 tens and 4 ones to the left of the point; to the right of the point we have: 4 tenths, 5 hundredth and 6 thousandths.
Learn more about: “Place value”. →
How do you read decimal numbers?
To say the amount of a number or to represent in written form it is possible by two common methods.
 Common mention of the number and the point of division, for example:
25.67 → Twentyfive point sixtyseven.
0.47 → point forty seven.
100.100 → One hundred point one.
18.18 → eighteen point eighteen.  By positioning the last number to the right of the point, for example:
25.67 → Twentyfive integers, sixtyseven hundredths.
0.47 → forty seven hundredths.
100.100 → One hundred integers, one tenth.
18.18 → eighteen integers, eighteen hundredths.Note: Instead of writing "integers" it can be represented as "units."
Operations with decimal numbers
The four operations with fundamental decimals are addition, subtraction, division and multiplication.
Addition and Subtraction with decimal point
When making sums with numbers with decimals, it is important to align the numbers according to the position of each number: The ones must be with the ones, tens with tens corresponding to the left of the point, to the right of the point must be the tenths with tenths, hundredths with hundredths and so on.
Examples:
Learn more about: “Sum”. →
Learn more about: “Subtraction”. →
Multiplication with decimal point
When multiplying a number it is important to consider at the end of the operation the position of the point, for the placement of the point the spaces to the right of the decimal point of the numbers that are being multiplied are counted.
Examples:
The red number represents the offset of the point.
Learn more about: “Multiplication”. →
Division with decimal point
The divisions with decimal point are very simple, we just have to place the decimal point in the quotient part, in other words the point goes up from the dividend to the quotient.
Learn more about: “Division”. →
Content
Arithmetic Tutorials
 Arithmetic
 Number
 Natural
 Integer
 Rational
 Irrational
 Complex
 Even
 Odd
 Prime
 Decimal
 Ordinal
 Pi number
 Euler number
 Golden number
 Place value
 Sum
 Subtraction
 Multiplication
 Division
 Rule of signs
 Signs of greater and lesser
 Absolute value
 Fraction
 Multiples
 Least common multiple (lcdm)
 Divisor
 Greatest common divisor (gcd)
 Exponent
 Logarithm
 Root (square y cube)
 Factorial
 Percentage
 Rule of three