This MCQ module is based on: Venn Diagrams, Union, Intersection, Complement
Venn Diagrams, Union, Intersection, Complement
This mathematics assessment will be based on: Venn Diagrams, Union, Intersection, Complement
Targeting Class 11 level in Sets, with Advanced difficulty.
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1.9 Venn Diagrams
Most of the relationships between sets can be represented by means of diagrams known as Venn diagrams?. These diagrams are named after the English logician John Venn (1834–1883). In Venn diagrams, the universal set is represented by a rectangle and its subsets by circles (or closed curves) drawn inside the rectangle.
The reader will see an extensive use of Venn diagrams when we discuss the union, intersection and difference of sets.
1.10 Operations on Sets
In earlier classes, we learned how to perform the operations of addition, subtraction, multiplication and division on numbers. Each of these operations was performed on a pair of numbers to get another number. Similarly, there are some operations which when performed on two sets give rise to another set. We now define certain operations on sets and examine their properties.
1.10.1 Union of Sets
Example 12
Let \(A = \{2, 4, 6, 8\}\) and \(B = \{6, 8, 10, 12\}\). Find \(A \cup B\).
Example 13
Let \(A = \{a, e, i, o, u\}\) and \(B = \{a, i, u\}\). Show that \(A \cup B = A\).
Example 14
Let X = {Ram, Geeta, Akbar} be the set of students of Class XI who are in the school hockey team. Let Y = {Geeta, David, Ashok} be the set of students from Class XI who are in the school football team. Find \(X \cup Y\) and interpret the set.
- \(A \cup B = B \cup A\) (Commutative law)
- \((A \cup B) \cup C = A \cup (B \cup C)\) (Associative law)
- \(A \cup \emptyset = A\) (Law of identity element; \(\emptyset\) is the identity of \(\cup\))
- \(A \cup A = A\) (Idempotent law)
- \(U \cup A = U\) (Law of U)
1.10.2 Intersection of Sets
Example 15
Consider the sets A and B of Example 12. Find \(A \cap B\).
Example 16
Consider the sets X and Y of Example 14. Find \(X \cap Y\).
Example 17
Let \(A = \{1, 2, 3, 4, 5, 6, 7, 8, 9, 10\}\) and \(B = \{2, 3, 5, 7\}\). Find \(A \cap B\) and hence show that \(A \cap B = B\).
- \(A \cap B = B \cap A\) (Commutative law)
- \((A \cap B) \cap C = A \cap (B \cap C)\) (Associative law)
- \(\emptyset \cap A = \emptyset\), \(U \cap A = A\) (Law of \(\emptyset\) and U)
- \(A \cap A = A\) (Idempotent law)
- \(A \cap (B \cup C) = (A \cap B) \cup (A \cap C)\) (Distributive law — \(\cap\) distributes over \(\cup\))
1.10.3 Difference of Sets
Example 18
Let \(A = \{1, 2, 3, 4, 5, 6\}\), \(B = \{2, 4, 6, 8\}\). Find \(A - B\) and \(B - A\).
Example 19
Let \(V = \{a, e, i, o, u\}\) and \(B = \{a, i, k, u\}\). Find \(V - B\) and \(B - V\).
1.11 Complement of a Set
Let U be the universal set which consists of all those prime numbers that are not divisors of 42. Thus, \(A = \{x : x \in U \text{ and } x \text{ is not a divisor of } 42\}\). We see that 2 is a divisor of 42. Similarly, 3 is a divisor of 42, and 7 is a divisor of 42. Now 2, 3 and 7 are the only elements of U which do not belong to A. The set \(\{2, 3, 7\}\) is called the Complement? of A with respect to U.
Example 20
Let \(U = \{1, 2, 3, 4, 5, 6, 7, 8, 9, 10\}\) and \(A = \{1, 3, 5, 7, 9\}\). Find \(A'\).
Example 21
Let U be the universal set of all the students of Class XI of a coeducational school and A be the set of all girls in Class XI. Find \(A'\).
Example 22 — De Morgan's Laws in Action
Let \(U = \{1, 2, 3, 4, 5, 6\}\), \(A = \{2, 3\}\) and \(B = \{3, 4, 5\}\). Find \(A'\), \(B'\), \(A' \cap B'\), \(A \cup B\) and hence show that \((A \cup B)' = A' \cap B'\).
Hence \(A' \cap B' = \{1, 6\}\).
Also \(A \cup B = \{2, 3, 4, 5\}\), so \((A \cup B)' = \{1, 6\}\).
Therefore, \((A \cup B)' = A' \cap B'\). This verifies De Morgan's Law.
- Complement laws: (i) \(A \cup A' = U\) (ii) \(A \cap A' = \emptyset\)
- De Morgan's laws: (i) \((A \cup B)' = A' \cap B'\) (ii) \((A \cap B)' = A' \cup B'\)
- Law of double complementation: \((A')' = A\)
- Laws of empty set and universal set: \(\emptyset' = U\) and \(U' = \emptyset\)
Exercise 1.4
(i) \(X = \{1, 3, 5\}\), \(Y = \{1, 2, 3\}\)
(ii) \(A = \{a, e, i, o, u\}\), \(B = \{a, b, c\}\)
(iii) \(A = \{x : x \text{ is a natural number and multiple of } 3\}\), \(B = \{x : x \text{ is a natural number less than } 6\}\)
(iv) \(A = \{x : x \text{ is a natural number and } 1 \lt x \leq 6\}\), \(B = \{x : x \text{ is a natural number and } 6 \lt x \lt 10\}\)
(v) \(A = \{1, 2, 3\}\), \(B = \emptyset\)
(ii) \(A \cup B = \{a, b, c, e, i, o, u\}\)
(iii) \(A = \{3, 6, 9, 12, \ldots\}\), \(B = \{1, 2, 3, 4, 5\}\). \(A \cup B = \{1, 2, 3, 4, 5, 6, 9, 12, \ldots\}\) = \(\{x : x \in \mathbb{N} \text{ and } (x \lt 6 \text{ or } 3 | x)\}\)
(iv) \(A = \{2, 3, 4, 5, 6\}\), \(B = \{7, 8, 9\}\). \(A \cup B = \{2, 3, 4, 5, 6, 7, 8, 9\}\)
(v) \(A \cup B = \{1, 2, 3\} \cup \emptyset = \{1, 2, 3\}\)
\(A \cup B = \{a, b, c\} = B\). (When \(A \subset B\), \(A \cup B = B\).)
(i) \(A \cup B\) (ii) \(A \cup C\) (iii) \(B \cup C\) (iv) \(B \cup D\)
(v) \(A \cup B \cup C\) (vi) \(A \cup B \cup D\) (vii) \(B \cup C \cup D\)
(v) \(\{1,2,3,4,5,6,7,8\}\) (vi) \(\{1,2,3,4,5,6,7,8,9,10\}\) (vii) \(\{3,4,5,6,7,8,9,10\}\)
(iv) \(A \cap B = \emptyset\) (A goes up to 6, B starts from 7; but wait — \(A = \{2,3,4,5,6\}\) and \(B = \{7,8,9\}\), so indeed \(A \cap B = \emptyset\))
(v) \(A \cap B = \{1, 2, 3\} \cap \emptyset = \emptyset\)
(i) \(A \cap B\) (ii) \(B \cap C\) (iii) \(A \cap C \cap D\)
(iv) \(A \cap C\) (v) \(B \cap D\) (vi) \(A \cap (B \cup C)\)
(vii) \(A \cap D\) (viii) \(A \cap (B \cup D)\) (ix) \((A \cap B) \cap (B \cup C)\)
(x) \((A \cup D) \cap (B \cup C)\)
(iv) \(\{11\}\) (v) \(\emptyset\) (vi) \(B \cup C = \{7,9,11,13,15\}\), \(A \cap \{7,9,11,13,15\} = \{7,9,11\}\)
(vii) \(\emptyset\) (viii) \(B \cup D = \{7,9,11,13,15,17\}\), \(A \cap \{7,9,11,13,15,17\} = \{7,9,11\}\)
(ix) \(A \cap B = \{7,9,11\}\), \(B \cup C = \{7,9,11,13,15\}\), intersection = \(\{7,9,11\}\)
(x) \(A \cup D = \{3,5,7,9,11,15,17\}\), \(B \cup C = \{7,9,11,13,15\}\), intersection = \(\{7,9,11,15\}\)
Exercise 1.5
(i) \(A'\) (ii) \(B'\) (iii) \((A \cup C)'\) (iv) \((A \cup B)'\) (v) \((A')'\)
(vi) \((B - C)'\)
(ii) \(B' = \{1,3,5,7,9\}\)
(iii) \(A \cup C = \{1,2,3,4,5,6\}\), \((A \cup C)' = \{7,8,9\}\)
(iv) \(A \cup B = \{1,2,3,4,6,8\}\), \((A \cup B)' = \{5,7,9\}\)
(v) \((A')' = A = \{1,2,3,4\}\)
(vi) \(B - C = \{2,8\}\), \((B-C)' = \{1,3,4,5,6,7,9\}\)
(i) \(A = \{a, b, c\}\) (ii) \(B = \{d, e, f, g\}\)
(iii) \(C = \{a, c, e, g\}\) (iv) \(D = \{f, g, h, a\}\)
(ii) \(B' = \{a, b, c, h\}\)
(iii) \(C' = \{b, d, f, h\}\)
(iv) \(D' = \{b, c, d, e\}\)
(i) \(\{x : x \text{ is an even natural number}\}\)
(ii) \(\{x : x \text{ is an odd natural number}\}\)
(iii) \(\{x : x \text{ is a positive multiple of } 3\}\)
(iv) \(\{x : x \text{ is a prime number}\}\)
(v) \(\{x : x \text{ is a natural number divisible by } 3 \text{ and } 5\}\)
(vi) \(\{x : x \text{ is a perfect square}\}\)
(vii) \(\{x : x \text{ is a perfect cube}\}\)
(viii) \(\{x : x + 5 = 8\}\)
(ix) \(\{x : 2x + 5 = 9\}\)
(x) \(\{x : x \geq 7\}\)
(xi) \(\{x : x \in \mathbb{N} \text{ and } 2x + 1 \gt 10\}\)
(ii) \(\{x : x \text{ is an even natural number}\}\)
(iii) \(\{x : x \in \mathbb{N} \text{ and } x \text{ is not a multiple of } 3\}\)
(iv) \(\{x : x \text{ is a positive composite number or } x = 1\}\)
(v) \(\{x : x \in \mathbb{N} \text{ and } x \text{ is not divisible by both } 3 \text{ and } 5\}\)
(vi) \(\{x : x \in \mathbb{N} \text{ and } x \text{ is not a perfect square}\}\)
(vii) \(\{x : x \in \mathbb{N} \text{ and } x \text{ is not a perfect cube}\}\)
(viii) \(x + 5 = 8 \Rightarrow x = 3\). Complement = \(\{x : x \in \mathbb{N} \text{ and } x \neq 3\}\)
(ix) \(2x + 5 = 9 \Rightarrow x = 2\). Complement = \(\{x : x \in \mathbb{N} \text{ and } x \neq 2\}\)
(x) \(\{x : x \in \mathbb{N} \text{ and } x \lt 7\} = \{1, 2, 3, 4, 5, 6\}\)
(xi) \(2x + 1 \gt 10 \Rightarrow x \gt 4.5 \Rightarrow x \geq 5\). Complement = \(\{1, 2, 3, 4\}\)
- Draw two identical Venn diagrams: a rectangle U containing two overlapping circles A and B.
- On the first diagram, shade everything OUTSIDE both circles. This is \((A \cup B)'\).
- On the second diagram, first shade \(A'\) (everything outside A) lightly, then shade \(B'\) (everything outside B) lightly. The region where BOTH shadings overlap is \(A' \cap B'\).
- Compare the two diagrams. Are the shaded regions identical?
- Repeat for the second De Morgan's law: compare \((A \cap B)'\) with \(A' \cup B'\).
Observe: Both diagrams give exactly the same shaded region! This visually confirms De Morgan's first law: \((A \cup B)' = A' \cap B'\).
Explain: An element is outside \(A \cup B\) if and only if it is outside A AND outside B. "Not in A or B" means "not in A" AND "not in B".
Students who like at least one subject: 170.
Students who like neither: \(n((M \cup S)') = n(U) - n(M \cup S) = 200 - 170 = \mathbf{30}\).
\(n(M - S) = n(M) - n(M \cap S) = 120 - 40 = 80\).
\(n(S - M) = n(S) - n(M \cap S) = 90 - 40 = 50\).
Verification: \(80 + 40 + 50 + 30 = 200 = n(U)\). The four disjoint regions (M only, both, S only, neither) partition U.
M only: \(n(M - S) = 80\) students
Both: \(n(M \cap S) = 40\) students
S only: \(n(S - M) = 50\) students
Neither: \(n((M \cup S)') = 30\) students
Total: 80 + 40 + 50 + 30 = 200.
STEM Fair formula: Invite = \(M \cup S\). Number to invite = \(n(M \cup S) = n(M) + n(S) - n(M \cap S) = 120 + 90 - 40 = 170\). Send invitations to 170 students.
Assertion–Reason Questions
Reason (R): This is De Morgan's first law and it holds for all sets A, B with respect to a universal set U.
Reason (R): The difference of sets is not commutative in general; \(A - B \neq B - A\) unless \(A = B\).
Reason (R): An element cannot simultaneously belong to a set and its complement.
Frequently Asked Questions
What are the basic operations on sets?
The basic set operations are union (elements in A or B or both), intersection (elements common to both), difference (elements in A but not in B), and complement (elements not in A). These are visualized using Venn diagrams.
What is a Venn diagram?
A Venn diagram is a visual representation of sets using circles inside a rectangle representing the universal set. Overlapping regions show common elements. Named after John Venn, they help visualize set operations.
What are De Morgan Laws in set theory?
De Morgan Laws state: the complement of A union B equals A-complement intersection B-complement, and the complement of A intersection B equals A-complement union B-complement.
What is the complement of a set?
The complement of set A with respect to universal set U is the set of all elements in U that are not in A. For example, if U = {1,2,3,4,5} and A = {1,3,5}, then A-complement = {2,4}.
How do you solve problems using Venn diagrams?
Draw the universal set as a rectangle, draw circles for each set, fill in the intersection region first, then remaining regions. Use the formula n(A union B) = n(A) + n(B) - n(A intersection B).
Frequently Asked Questions — Sets
What is Venn Diagrams, Union, Intersection, Complement in NCERT Class 11 Mathematics?
Venn Diagrams, Union, Intersection, Complement is a key concept covered in NCERT Class 11 Mathematics, Chapter 1: Sets. This lesson builds the student's foundation in the chapter by explaining the core ideas with worked examples, definitions, and step-by-step methods aligned to the CBSE curriculum.
How do I solve problems on Venn Diagrams, Union, Intersection, Complement step by step?
To solve problems on Venn Diagrams, Union, Intersection, Complement, follow the NCERT method: identify the given quantities, choose the relevant formula or theorem, substitute values carefully, and simplify. Class 11 exercises gradually increase in difficulty — start with solved NCERT examples before attempting exercise questions, and always verify your answer by substitution or diagram.
What are the most important formulas for Chapter 1: Sets?
The essential formulas of Chapter 1 (Sets) are listed in the chapter summary and highlighted throughout the lesson in formula boxes. Memorise them and practise at least 2–3 problems per formula. CBSE board exams frequently test direct application as well as combined use of multiple formulas from this chapter.
Is Venn Diagrams, Union, Intersection, Complement important for the Class 11 board exam?
Venn Diagrams, Union, Intersection, Complement is part of the NCERT Class 11 Mathematics syllabus and appears in CBSE board exams. Questions typically include short-answer, long-answer, and competency-based items. Review the NCERT examples, exercise questions, and previous-year board problems on this topic to prepare confidently.
What mistakes should students avoid in Venn Diagrams, Union, Intersection, Complement?
Common mistakes in Venn Diagrams, Union, Intersection, Complement include skipping steps, misapplying formulas, sign errors, and losing track of units. Write each step clearly, double-check algebraic manipulations, and re-read the question after solving to verify that your answer matches what was asked.
Where can I find more NCERT practice questions on Venn Diagrams, Union, Intersection, Complement?
End-of-chapter NCERT exercises for Venn Diagrams, Union, Intersection, Complement cover all difficulty levels tested in CBSE exams. After completing them, try the examples again without looking at the solutions, attempt the NCERT Exemplar questions for Chapter 1, and solve at least one previous-year board paper to consolidate your understanding.