Random Variables /Part2

Random Variabl
A random variable , usually written as X, is a variable whose values are the numberical values of arandom phenomenon.Ther are two types of a random variable, discrete and continuous.
The discrete random variable
is a variable which may take only countable number of distinct values such as 0,1,2,3,...

Examples of discrete random variables include the number of children in a family, , the number of patients in a doctor s surgery, the number of defective light bulbs in a box of ten.
The probability distribution of a discrete random variable is a list of probabilities associated with each of its possible values. It is also sometimes called the probability function or the probability mass function.
(Definitions taken from Valerie J. Easton and John H. McColl s Statistics Glossary v1.1)
Suppose a random variable X may take k different values, with the probability that X = xi defined to be P(X = xi) = pi.

The probabilities pi must satisfy the following:
the sum of P(x=X)=1