Complete Guide For Class 8th Math Chapter 1 – Rational Numbers

Welcome to iPrep, your Learning Super App. Our learning resources for the chapter, Rational Numbers in Mathematics Class 8th Chapter 1 are designed to ensure that you grasp this concept with clarity and perfection based on NCERT Curriculum. Whether you’re studying for an upcoming exam or strengthening your concepts, our engaging animated videos, practice questions and notes offer you the best of integrated learning with interesting explanations and examples.

The concept of rational numbers in Class 8 Mathematics introduces students to numbers expressed as fractions or ratios, including positive and negative values. The curriculum covers operations, comparisons, and representations on the number line, enhancing numerical understanding and problem-solving skills. Let’s start with understanding what are rational numbers. 

Rational Numbers 

Rational Numbers are numbers that can be expressed in the form of p/q where p and q are integers and q≠0. This chapter introduces the concept and various properties of rational numbers.

Understanding Rational Numbers

Now that we know what are rational numbers, we will look at some of the subsets of rational numbers. 

Rational numbers encompass various subsets of numbers, including integers, whole numbers, and fractional numbers. Here’s a brief breakdown:

• Natural Numbers: The set of positive integers starting from 1.
• Whole Numbers: The set of natural numbers including 0.
• Integers: The set of whole numbers and their negatives.
• Fractional Numbers: Numbers expressed as fractions or decimals.

Properties of Rational Numbers

The set of rational numbers exhibits several fundamental properties, which are essential for understanding and performing mathematical operations. Let’s explore these properties of rational numbers for class 8 chapter 1 in detail:

Closure Property

For any two rational numbers a and b:

• a+b is a rational number.
• a−b is a rational number.
• a×b is a rational number.
• a÷b (where b≠0) is a rational number.

Commutative Property

For any two rational numbers a and b:

• a+b = b+a
• a×b = b×a

Associative Property

For any three rational numbers a, b, and c:

• (a+b)+c = a+(b+c)
• (a×b)×c = a×(b×c)

Additive and Multiplicative Identities

• Additive Identity: For every rational number a, a + 0 = 0 + a = a.
• Multiplicative Identity: For every rational number a, a×1 =  1×a = a.

Additive and Multiplicative Inverses

• Additive Inverse: For a rational number p/q​, the additive inverse is −p/q, satisfying p/q+(-p/q)=0 
• Multiplicative Inverse: For a non-zero rational number p/q, the multiplicative inverse is q/p​, satisfying q/p​×p/q​=1.

Distributive Property

For all rational numbers a, b, and c:

• a×(b+c) = (a×b) + (a×c)
• a×(b−c) = (a×b) − (a×c)

Representation of Rational Numbers on the Number Line

Now that we know all the properties of rational numbers in class 8 Chapter 1 mathematics, let’s now learn how to represent these rational numbers on a number line.

Rational numbers can be represented on a number line, extending both left (negative) and right (positive) from zero. Here’s how different sets of numbers are represented:

• Natural Numbers: Start from 1 and extend rightward.
• Whole Numbers: Start from 0 and extend rightward.
• Integers: Extend both left and right from zero.
• Rational Numbers: Include all possible fractions, positive and negative, and extend on both sides of zero.

Example Representations

• Rational Number −5/12: This lies between -1 and 0.

• Rational Number 8/3​: This lies between 2 and 3.

Finding Rational Numbers Between Two Rational Numbers:

We already know how to represent rational numbers on the number line, we will now learn how to calculate rational numbers between two rational numbers.

To find rational numbers between any two given rational numbers a and b, calculate:

• The average: a+b/2
• Continue finding more numbers by averaging between a and a+b/2​, and a+b/2 and b, so on.

Example: Finding Numbers Between 1/5​ and 3/8

To find two rational numbers between 1/5 and 3/8:

1. Calculate 1/5+ 3/8​ divided by 2, which gives 23/80.
2. Further, find numbers between 1/5​ and 23/80, and 23/80​ and 3/8.

This comprehensive guide provides a thorough understanding of rational numbers, their properties, and their representation. These foundational concepts are crucial for further exploration in mathematics.