NCERT Book Class 7 Maths Chapter 8 Rational Numbers

124 MATHEMATICS

Chapter 8
Rational
Numbers
8.1 INTRODUCTION
You began your study of numbers by counting objects around you. The
numbers used for this purpose were called counting numbers or natural
numbers. They are 1, 2, 3, 4, ... By including 0 to natural numbers, we
got the whole numbers, i.e., 0, 1, 2, 3, ... The negatives of natural
numbers were then put together with whole numbers to make up
integers. Integers are ..., –3, –2, –1, 0, 1, 2, 3, .... We, thus, extended
the number system, from natural numbers to whole numbers and from
whole numbers to integers.
numerator
You were also introduced to fractions. These are numbers of the form ,
denominator
where the numerator is either 0 or a positive integer and the denominator, a positive integer.
You compared two fractions, found their equivalent forms and studied all the four basic
operations of addition, subtraction, multiplication and division on them.
In this Chapter, we shall extend the number system further. We shall introduce the concept
of rational numbers alongwith their addition, subtraction, multiplication and division operations.

8.2 NEED FOR RATIONAL NUMBERS
Earlier, we have seen how integers could be used to denote opposite situations involving
numbers. For example, if the distance of 3 km to the right of a place was denoted by 3, then
the distance of 5 km to the left of the same place could be denoted by –5. If a profit of ` 150
was represented by 150 then a loss of ` 100 could be written as –100.
There are many situations similar to the above situations that involve fractional numbers.
3
You can represent a distance of 750m above sea level as km. Can we represent 750m
4
3 −3
below sea level in km? Can we denote the distance of km below sea level by ? We can
4 4
−3
see is neither an integer, nor a fractional number. We need to extend our number system
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to include such numbers.