Answer:
Probability by definition is the extent to which an event is likely to occur, measured by the ratio of the favourable cases to the whole number of cases possible.
Since number of elements in the set of favourable cases is less than or equal to the number of elements in the set of whole number of cases, their ratio would always end up being 1 or less than one.
Probability equals one when favourable number of cases are same as that of the whole number of cases and probability equals zero when there is no favourable case
