CBSE Class 11 Mathematics Chapter 6: Linear Inequalities NCERT Solutions

NCERT Solutions PDF Class 11 PDF

This chapter provides comprehensive NCERT Solutions for Class 11 Mathematics, focusing on Chapter 6: Linear Inequalities. It covers solving linear inequalities in one variable for different sets of numbers, including natural numbers, integers, and real numbers. The solutions detail the step-by-step process of isolating the variable, considering the impact of multiplying or dividing by negative numbers, and representing the solution sets. These solutions are designed to help students understand the fundamental concepts of linear inequalities and build a strong foundation for more advanced topics in algebra. They are an excellent resource for exam preparation, offering clear explanations and accurate answers to all exercise problems, ensuring students can confidently tackle similar questions in their assessments.

Quick info

BoardCBSE
ClassClass 11
SubjectMathematics
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 6: Linear Inequalities

Chapter summary

Chapter 6 of the Class 11 NCERT Mathematics textbook introduces the concept of linear inequalities in one variable. This section provides detailed solutions for Exercise 6.1, focusing on solving inequalities for various number sets like natural numbers, integers, and real numbers. It emphasizes the algebraic manipulation required to find the solution set and understand the graphical representation of these solutions on a number line.

Learning outcomes

  • Understand the concept of linear inequalities in one variable.
  • Solve linear inequalities for natural numbers.
  • Solve linear inequalities for integers.
  • Solve linear inequalities for real numbers.
  • Apply algebraic methods to find solution sets of inequalities.
  • Represent solution sets on a number line.

Topics covered

Paper topics

  • Introduction to Linear Inequalities
  • Solving Linear Inequalities in One Variable
  • Natural Number Solutions
  • Integer Solutions
  • Real Number Solutions
  • Algebraic Manipulation of Inequalities
  • Inequality Sign Reversal
  • Solution Sets

Important topics

  • Solving inequalities for real numbers
  • Understanding the effect of multiplying/dividing by negative numbers
  • Identifying solution sets for integers
  • Representing solutions on a number line

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Questions and Solutions

Exercise 6.1

Question 1

Solve the inequality 24x < 100, when:

(i) x is a natural number

(ii) x is an integer

Solution:

The given inequality is 24x < 100.

To solve for x, we divide both sides by 24. Since 24 is a positive number, the direction of the inequality sign remains unchanged.

\frac{24x}{24} < \frac{100}{24}

x < \frac{100}{24}

Simplifying the fraction \frac{100}{24} by dividing both the numerator and the denominator by their greatest common divisor, which is 4, we get:

x < \frac{25}{6}

Now, we consider the two cases:

(i) When x is a natural number:

Natural numbers are positive integers starting from 1 (i.e., 1, 2, 3, ...). We need to find the natural numbers that are less than \frac{25}{6}. Since \frac{25}{6} is approximately 4.17, the natural numbers satisfying this condition are 1, 2, 3, and 4.

Thus, the solution set when x is a natural number is \{1, 2, 3, 4\}.

(ii) When x is an integer:

Integers include positive numbers, negative numbers, and zero (i.e., ..., -3, -2, -1, 0, 1, 2, 3, ...). We need to find all integers that are less than \frac{25}{6} (approximately 4.17).

These integers are ..., -3, -2, -1, 0, 1, 2, 3, and 4.

Thus, the solution set when x is an integer is \{..., -3, -2, -1, 0, 1, 2, 3, 4\}.

Question 2

Solve the inequality -12x > 30, when:

(i) x is a natural number

(ii) x is an integer

Solution:

The given inequality is -12x > 30.

To solve for x, we divide both sides by -12. When dividing an inequality by a negative number, we must reverse the direction of the inequality sign.

\frac{-12x}{-12} < \frac{30}{-12}

x < \frac{30}{-12}

Simplifying the fraction \frac{30}{-12} by dividing both the numerator and the denominator by their greatest common divisor, which is 6, we get:

x < -\frac{5}{2}

Now, we consider the two cases:

(i) When x is a natural number:

Natural numbers are positive integers (1, 2, 3, ...). We need to find natural numbers that are less than - \frac{5}{2} (which is -2.5). Since there are no positive integers less than a negative number, there is no solution in the set of natural numbers.

Thus, when x is a natural number, there is no solution to the given inequality.

(ii) When x is an integer:

Integers include positive, negative, and zero values. We need to find all integers that are less than - \frac{5}{2} (which is -2.5).

The integers satisfying this condition are ..., -5, -4, -3.

Thus, the solution set when x is an integer is \{..., -5, -4, -3\}.

Question 3

Solve the inequality 5x - 3 < 7, when:

(i) x is an integer

(ii) x is a real number

Solution:

The given inequality is 5x - 3 < 7.

First, we isolate the term with x by adding 3 to both sides of the inequality. Since 3 is positive, the inequality sign remains the same.

5x - 3 + 3 < 7 + 3

5x < 10

Next, we solve for x by dividing both sides by 5. Since 5 is a positive number, the inequality sign remains unchanged.

\frac{5x}{5} < \frac{10}{5}

x < 2

Now, we consider the two cases:

(i) When x is an integer:

We need to find all integers that are strictly less than 2. These integers are ..., -4, -3, -2, -1, 0, and 1.

Thus, the solution set when x is an integer is \{..., -4, -3, -2, -1, 0, 1\}.

(ii) When x is a real number:

When x is a real number, the solution includes all real numbers that are strictly less than 2. This can be represented as an open interval on the number line.

Thus, the solution set when x is a real number is x \in (-\infty, 2).

Question 4

Solve the inequality 3x + 8 > 2, when:

(i) x is an integer

(ii) x is a real number

Solution:

The given inequality is 3x + 8 > 2.

To solve for x, we first subtract 8 from both sides of the inequality. Since 8 is positive, the inequality sign does not change.

3x + 8 - 8 > 2 - 8

3x > -6

Now, we divide both sides by 3. Since 3 is a positive number, the inequality sign remains the same.

\frac{3x}{3} > \frac{-6}{3}

x > -2

Now, we consider the two cases:

(i) When x is an integer:

We need to find all integers that are strictly greater than -2. These integers are -1, 0, 1, 2, 3, and so on.

Thus, the solution set when x is an integer is \{-1, 0, 1, 2, 3, ...\}.

(ii) When x is a real number:

When x is a real number, the solution includes all real numbers that are strictly greater than -2. This can be represented as an open interval on the number line.

Thus, the solution set when x is a real number is x \in (-2, \infty).

Common mistakes

  • Forgetting to reverse the inequality sign when multiplying or dividing by a negative number.
  • Incorrectly identifying the set of numbers (natural, integer, real) for the solution.
  • Errors in simplifying fractions or performing arithmetic operations.
  • Not considering the domain of the variable (e.g., natural numbers vs. integers).

Revision tips

  • Review the rules for manipulating inequalities, especially when multiplying or dividing by negative numbers.
  • Practice solving inequalities for different types of number sets (natural, integer, real).
  • Pay close attention to the boundary points and whether they are included in the solution set.
  • Visualize the solution set on a number line to reinforce understanding.

Practice MCQs

Q1. What is the solution set for 24x < 100 when x is a natural number?

Q2. When solving -12x > 30 for an integer x, what is the correct inequality after dividing by -12?

Q3. What is the solution set for 5x - 3 < 7 when x is an integer?

Q4. The solution set for 3x + 8 > 2 when x is a real number is represented as:

Q5. Which type of number set has no solution for the inequality -12x > 30?

Frequently asked questions

What is the main focus of Chapter 6: Linear Inequalities for Class 11 Maths?

This chapter focuses on understanding and solving linear inequalities in one variable for different sets of numbers, including natural numbers, integers, and real numbers, using algebraic methods.

How do the NCERT Solutions help in solving linear inequalities?

The NCERT Solutions provide clear, step-by-step explanations for each problem, demonstrating how to manipulate inequalities and determine the correct solution set for various number types.

What is the key difference when solving inequalities for integers versus real numbers?

For integers, the solution is a discrete set of whole numbers. For real numbers, the solution is typically an interval, representing all numbers within a certain range.

Why is it important to reverse the inequality sign?

The inequality sign must be reversed when multiplying or dividing both sides of the inequality by a negative number to maintain the truth of the statement.

Are graphical representations included in these solutions?

While the provided solutions focus on algebraic methods, understanding the solution set on a number line is often implied, especially when dealing with real numbers.

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