There are many
situations where we have an intuitive idea of how likely they are
to happen based on past experience.

We may, for example, look at the
sky and the barometer and decide that there is a good chance that
it will rain. Mathematician try to put a number to such an event
to give a clearer idea of how likely it is to happen. When an event
is a certainty, such as the chance that you will die one day, it
is given the number 1. When the chance of an event happening is
zero, such as you swimming the Atlantic ocean, then it is given
the number 0. tossing a coin to see whether it come up head or tail
is used to start many games because the likelihood of either happening
is the same, so it is the given number 1/2 .This numerical
value of the likelihood of an event happening is called its probability,
and it always takes a value between 0 and 1.

Generally,
the probability of a particular outcome for equally likely events
is given by

When a die is rolled
there are six possible outcomes which are all equally likely, so
as only one of these gives a 5 uppermost, the probability of scoring
a 5 is said to be 1/6 . In a standard pack of 52 playing cards there
are 4 kings, so the probability that if you take one card from the
pack it will be a king is 4/52 = 1/13. The probability of drawing
a prime number from the pack would be 16/52 = 4/13, as there are
16 prime numbers in the pack, namely the 2,3,5 and 7 of clubs, hearts,
diamonds and spades

Probability is
also determined by keeping records of similar events over a long
run.

For example, a sheep farmer may know from her records that
on average one-third of her ewes have twin lamps, so she would give
the probability of having twins at each birth as 1/3.