Probability
Tossing a coin, keeping an object in a box, selecting a student from a group of students , rolling a dice are all processes which have a number of possible outcomes . The two possible outcomes of tossing a coin are heads and tails, rolling a dice has six outcomes, a student can be selected from a group of students in many ways. So to arrive at an answer its best to follow the rules of probability.
Notations:
If n belongs to N ( N = { set of natural numbers} ) then the product 1x2x3x4x.....n is denoted by n! and read as n factorial .
Fundamental theorems of probability
 Fundamental principle of addition:
If one thing can be done in m different ways and the other thing can be done in n different ways independent of the first then either of them can be done in ( m+n) different ways.
eg :a) select a king or a queen from a pack of 52 cards
a king can be selected in 4 ways . m= 4
a queen can be selected in 4 ways . n= 4
so either can be selected in (4 + 4) = 8 ways
 Fundamental principle of multiplication:
If one thing can be done in m different ways and another thing can be done in n different ways independent of the first then both the things can be done in mxn different ways .
eg: a) select a king and a queen from a pack of 52 cards
a king can be selected in 4 ways . m=4
a queen can be selected in 4 ways . n=4
so both can be selected in (4x4) = 16 ways
