**INTRODUCTION **

Often experiments are performed in order to produce observations or measurements that assist us in arriving at conclusions. These recorded informations in it’s original collected form are referred as ” raw data ” .

Mathematicians define experiment as any process or operation that generates raw data.

If a chemist runs an analysis several times under the same experimental conditions, he will not get concurrent result, which indicates an element of chance in the experimental procedure.

It is these chance outcomes that occur around us with which this chapter is basically concerned.

__Random Experiment:__

An experiment, whose all possible outcomes are known in advance but the outcome of any specific performance can not be predicted before the completion of the experiment, is known as random experiment.

An example of random experiment might be tossing of a coin. This experiment consists of only two outcomes head or tail. Another example might be launching of a missile and observing the velocity at specified times. The opinions of voters concerning a new sales tax can also be considered as outcomes of random experiment.

__Sample-space and sample point:__

A set whose elements represent all possible outcomes of a random experiment is called the sample space and is usually represented by ‘ S ‘.

An element of a sample space is called a sample point.

Consider the experiment of tossing a die. If we are interested in the number that shows on the top face, then sample space would be S_{1} = {1, 2, 3, 4, 5, 6}

If we are interested only in whether the number is even or odd, then sample space is simply S_{2} = {even, odd}

Clearly more than one sample space can be used to describe the outcomes of an experiment. In this case ‘ S_{1} ‘ provides more information than ‘ S_{2} ‘. If we know which element in S_{1} occurs, we can tell which outcome in S_{2} occurs; however, a knowledge of what happens in S_{2} in no way helps us to know which element in S_{1} occurs.

In general it is desirable to use a sample space that gives the maximum information concerning the outcomes of the experiment.

Suppose three items are selected at random from a manufacturing process. Each item is inspected and classified as defective or non-defective. The sample providing the maximum information would be S_{1} = {NNN, NDN, DNN, NND, DDN, DND, NDD, DDD}.

A second sample space, although it provides, less information, might be S_{2} = {0, 1, 2, 3} Where the elements represent no defectives, one defective, two defectives, or three defectives in our random selection of three items.