That's simple
Real numbers can either be rational or irrational. ... A rational number is a numberwhich can be written as a ratio of two whole numbers (integers). For example 5 is arational number since 5 can be written as ratio of 5 : 1 . 5 is also an integer. 2.5 is arational number since it is a ratio of 5 : 2 .
Hope it helps :)