In real time case Probability is the chance where something will happen, but here probability is a mathematical expression that deals with calculating the occurrence of any event.
That means an event which can produce some well defined outcomes but the exact output cannot be predicted in advance.
An operation which results in somewell defined outcomes is called as experiment.
The set of all posssible outcomes from a random experiment is called as Sample space.
It is usally denoted by S.
Any subset of a sample space is called an event
(i) When a coin is tossed, sample space S={H, T}
(ii) When two coins are tossed,
sample space S={HH, HT, TH, TT}
