Rational numbers

                      A rational number is a number that can be expressed in the form p/q where p and q are integers and q not = 0.

                       for example: -17, 1 3/4, 1.25  are rational numbers. The set of rational numbes is denoted by Q.

Irrational numbers

                  An irrational numbers are those which cannot be expressed in the form of the ratio of two integers.

                  for example: sqrt(3) , pi. It is denoted by Q'

Real numbers

                Real numbers are the union of sets of rational and irrational numbers. QUQ' = R.