Counting numbers are called natural numbers. It is denoted by N. N=(1,2,3,4………………)
Natural numbers together with 0 are called whole numbers. It is denoted by W. W=(0,1,2,3,4……………..)
The numbers less than 0 are called negative numbers. -1,-2,-3,-4……….
The collection of whole numbers and negative numbers are called integers. It is denoted by I or Z. I or Z=(………. -3,-2,-1,0,1,2,3,4……….)
The numbers which can be written in the form of p/q, where q≠0 and p,q are integers are called rational numbers. It is denoted by Q. for example:- -1/2,-5/7, 2/3,0/1 etc.
Closure property
So rational numbers are closed under addition. If a and b are any two rational numbers, then a+b is also a rational number.
So rational numbers are closed under subtraction. If a and b are any two rational numbers, then a-b is also a rational number.
So rational numbers are closed under multiplication. If a and b are any two rational numbers, then axb is also a rational number.
7÷0=not defined So for any rational number a, a÷0 is not defined. So rational numbers are not closed under division. If a and b are any two rational numbers, then a÷b is not a rational number.