This article is about the concepts of probability.
We use the term probability when we deal with random events. Events are said to be random when the conditions for their occurrence are unknown for some reason or other and which cannot therefore be predicted before hand with certainty.
When you purchase a bus ticket, we do not know beforehand if its number will be even or odd. When we toss a coin we cannot predict if it will fall head up or tail up. Both the events, acquiring a ticket with an even number for tossing a coin with head up are random events. If we acquire say 10 bus tickets (not all at once) it might turn out that all the 10 are with even number or none at all. But there is a definite law in this apparent mess. If we repeat our trial of acquiring tickets a sufficiently great number of times then in about one-half of the total trials our ticket will have an even number. So the probability of getting a ticket with an even number is one half. Similarly in tossing a coin we can be sure that it will fall head up in about half of all the cases provided we toss many times. We may therefore define probability as follows
Thermal physics —A.B. Gupta , H.P. Roy