event

Equally likely events

• Two or more events are said to be equally likely if each one of them has an equal chance of occurring.
• Head and tail are equally likely events in tossing a coin.

Certain events

• In an experiment, the event which surely occur is called certain event.
• When we roll a die, the event of getting any natural number from one to six is a certain event.

Impossible events

• In an experiment if an event has no scope to occur then it is called an impossible event.
• When we toss two coins, the event of getting three heads is an impossible event.

Mutually exclusive events

• Two or more events are said to be mutually exclusive if they don’t have common sample points.
• i.e., events A, B are said to be mutually exclusive if A ∩ B = Ø
• When we roll a die the events of getting odd numbers and even numbers are mutually exclusive events.

Exhaustive events

• The collection of events whose union is the whole sample space are called exhaustive events.
• When we toss a coin twice, the collection of events of getting two heads, exactly one head, no head are exhaustive events.

Complementary events

• The complement of an event A is the event representing collection of sample points not in A.
• It is denoted A’ or Ā
• The event A and its complement Ā are mutually exclusive and exhaustive.
• When we roll a die, the event ‘rolling a 5 or 6’ and the event of rolling a 1, 2, 3 or 4 are complementary events.

Elementary event:

• If an event E consists of only one outcome then it is called an elementary event.