# Number, Numeric, Quantity

A number is a mathematical object used to:

Example: When we are interested in the total number of each species of tortoise, or how many individuals there are per square kilometre.

This type of data is called commonly:

• numerical data
• or quantitative data.

The same number may be:

## 3 - Why

Number Type Equation they help to solve
Negative number `a + x = b`, even when `a > b`
Fractions `ax = b`, when `b` is not divisible by `a`
Reals `x² = 2`
Complex numbers `x² = -1`

## 4 - Notion

### 4.1 - Number System

Numbers can be classified into set, called number system.

The most common number system (ie number classification) are:

### 4.2 - Numeral System

Numbers can be expressed (ie written) into set, called numeral system (or system of numeration). It is a mathematical notation system for expressing numbers using digits (or other symbols).

Example of numeral system (ie number representation)]]:

### 4.3 - Number Storage

Numbers can be stored in:

However, since division almost immediately introduces infinitely repeating sequences of digits (such as 4/7 in decimal, or 1/10 in binary), the representation would be:

• truncated at some satisfactory size
• or else rational numbers would be used: a large integer for the numerator and for the denominator. But even with the greatest common divisor divided out, arithmetic with rational numbers can become unwieldy very quickly: 1/99 – 1/100 = 1/9900, and if 1/101 is then added the result is 10001/999900.

### 4.4 - Field

A field is a collection of “numbers” with their operator: +, -, *, /

### 4.5 - Discrete / Continous

Quantitative variables can be further categorized as either:

• discrete: those that can only have set, integral values, or discrete variables,
• or continuous: those that can be a range of values, or continuous variables. Quantitative Variables can be a range of values, or continuous variables.