Elementary Statistics and Computer Application

Definition of Probability

Mathematical (or) Classical (or) a-priori Probability:

• If an experiment results in ‘n’ exhaustive cases which are mutually exclusive and equally likely cases out of which ‘m’ events are favourable to the happening of an event ‘A’, then the probability ‘p’ of happening of ‘A’ is given by


Note

1. If m = 0 P(A) = 0, then ‘A’ is called an impossible event. (i.e.) also by P(Ø) = 0.
2. If m = n P(A) = 1, then ‘A’ is called assure (or) certain event.
3. The probability is a non-negative real number and cannot exceed unity (i.e.) lies between 0 to 1.
4. The probability of non-happening of the event ‘A’ (i.e.) P( Ā). It is denoted by ‘q’.
 
P(Ā ) =
q = 1 – p
p + q = 1
(or) P(A) + P(Ā ) = 1.