what do we mean by complementery events?
two events are complementary events if there are only two outcomes.
and if event 1 occur, event 2 will not occur.
1. the event that "it rains" and " it does not rain" are complementary events.
here only one of the two event occur .
no other event can occur
2. consider the tossing of the coin. either head comes or tail comes.
the result can be either head or tail (not both)
the result can not be anything except head or tail.
hope this helps you.