Quartiles is the four equal part of a population which is divided according to a particular variable. In statistics, Quartile divides the set of observation into 4 equal parts like how the median divides the set of observation into 2 equal parts, when arranged in the numerical order.
There are three points which divide the set of observation into 4 equal parts(as shown in the figure below). The three points are:
  1. First or Lower quartile (Q1)
  2. Second quartile or Median (Q2)
  3. Third quartile or Upper quartile (Q3)

Quartiles

The middle term value between the first term and the median is known as First or Lower quartile and is denoted as Q1. The formula is given as:

Quartile Formula
The median itself is known as Second quartile and is denoted as Q2. The formula is given as:

Quartile Formulas
The middle term value between the last term and the median is known as Third or Upper quartile and is denoted as Q3. The formula is given as:

Quartiles Formula