Q. Define natural numbers
Ans.
The natural numbers (also called the counting numbers) are the numbers that you "naturally" use for counting:
1,2,3,4,...
The set of natural numbers is closed under addition and multiplication: this means that when you add (or multiply) two natural numbers, you always get another natural number. However, it is not closed under division of subtraction. For example. If you divide 3 by 4, you get 0.75, which is not a natural number.