Probability Terminologies and Notations

We had several discussions about probability and before we delve deeper on this topic, let us reinforce our knowledge by familiarizing ourselves with the terminologies and notations used.   This is in preparation to more discussions ahead. Aside from probability, we will also learn more about permutations, combinations, statistics and other related fields. The following are the common terms used in probability as well as the notations used in most textbooks.



If a coin is tossed, when the coin comes to rest, it can show a tail or a head, each of which is an outcome.


Each roll of a die or toss of a coin is a trial.


An experiment consists of one or more trials.

Favorable Outcome

We roll die and we want to roll a six (we want six on the top face) and after rolling the six turned up, the six is a favourable outcome.

Equally likely outcome

Dice that are fair (not loaded) and cons that are fair (not bent), each outcome has an equal chance of turning up. The outcomes are equally likely.


When tossing a coin or rolling a die, we might want to roll a six or toss a head, each one is an event.


If a trial has N equally likely outcomes, then the probability of  any one of them is 1/N.


In our equations, we will use the notation P(event) to denote the probability of an event. Hence, the probability of getting a 4 in tossing a die is equal to 1/6 is denoted by

 P(4) = 1/6.


In some cases, we can also use the descriptive form of an event; for example,

P(ace of diamonds) = 1/4

can denote the probability of getting the ace of diamonds in well-shuffled pack of cards.

That’s all for now.  In the next post, to complete our preparation by studying set terminologies and notations.

Leave a Reply