A number which can be written in the form p/q , where p and q are integers and q ≠ 0 is called a rational number. For example,

2, 3, 6/7 are all rational numbers.

Since the numbers 0, –2, 4 can be written in the form p/q , they are also rational numbers.

Rational numbers are closed under addition. That is, for any two rational numbers a and b, a + b is also a rational number.

Rational numbers are closed under subtraction. That is, for any two rational numbers a and b, a – b is also a rational number.

Rational numbers are closed under multiplication. That is, for any two rational numbers a and b, a × b is also a rational number.

Rational numbers are not closed under division.

However, if we exclude zero ( because division by 0 is not defined.) then the collection of Rational numbers, all other rational numbers is closed under division.