Sets of numbers. Natural numbers: N. 0, 1, 2, 3, 4, ... Integer numbers: C 0, -1, 1, -2, 2, -3, 3,... Rational numbers: W. A rational number is any number that can be expressed as the fraction p/q, where p i q are integers and q not = 0. Examples: 0, 5, -4, 1/2, -2/3, 4 1/5. Irrational numbers: R\W. Examples: square root of 2, square root of 5, pi, 1 - square root of 7. Real numbers: R. Real numbers there are Rational and Irrational numbers.