Numbers can be grouped in to a number of sets. From the diagram you see that all rational numbers are also real numbers; i.e. ℚ is a subset of ℝ.
Positive integers
ℤ+ = {1, 2, 3, . . . }
Positive integers and zero
ℕ = {0,1,2,3,…}
Integers
ℤ = {…,−3,−2,−1,0,1,2,3,…}
Rational numbers
ℚ = any number that can be written as the ratio p/q of any two integers, where q ≠ 0