i) Variable and Constant:
1. A measurable quantity which can vary from one individual to another is called a ‘variable’. Examples are heights and weights of students in a class, prices of commodities, number of children in a family, etc. It is denoted by the last letters of alphabets, i.e., x, y, and z.
2. ‘Constant’ is a quantity which can assume only one value. Examples are p = 3.14159, e = 2.71828, etc. It is usually denoted by the first letters of alphabets, i.e., a, b, c, d, …ii) Continuous or Discrete Variables:
1. A variable which can assume any value within a given range is called a continuous variable. For example, the heights and weights of students, temperature, speed, etc. the height of a student can be 62”, 62.5” or 62.45”.
2. A variable which can assume only some specific values within a given range is called a discontinuous or discrete variable. For example, the number of houses in a town, number of children in a family, number of students in a class, etc. a discrete variable takes on values which are integers or whole numbers like 0,1,2,3,4,5, … but cannot be 2.5, 3.3, 3.91, 14.235, etc. There cannot be 4.5 houses in a town or 10.15 number of students in a class, etc.iii) Quantitative and Qualitative Data:
1. Quantitative variables are heights, weights, temperature, speed, etc.
2. Qualitative data are described by qualitative variables, such as marital status, religion, colour, race, etc.