NCERT Solutions for Class 9 Maths Unit 1
Number Systems Class 9
Unit 1 Number Systems Exercise 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 Solutions
The Natural Numbers
The natural (or counting) numbers are 1, 2, 3, 4, 5, etc. There are infinitely many natural numbers. The set of natural numbers is sometimes written N for short.
The whole numbers are the natural numbers together with 0.
The Integers
The integers are the set of real numbers consisting of the natural numbers, their additive inverses and zero. The set of integers is sometimes written J or Z for short. The sum, product, and difference of any two integers is also an integer.
But this is not true for division... just try 1 ÷ 2.
The Rational Numbers
The rational numbers are those numbers which can be expressed as a ratio between two integers. For example, the fractions 1/3 and –1111/8 are both rational numbers. All the integers are included in the rational numbers, since any integer z can be written as the ratio z/1.
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Exercise 1.1 : Solutions of Questions on Page Number : 5