Exercise 1.4 Sets
Question and Answers
Class 11 – Maths
| Class | Class 11 |
| Subject | Mathematics |
| Chapter Name | Sets |
| Chapter No. | Chapter 1 |
| Exercise | Exercise 1.4 |
| Category | Class 11 Maths NCERT Solutions |
Question 1 Find the union of each of the following pairs of sets :
(i) X = {1, 3, 5} Y = {1, 2, 3}
(i) X = {1, 3, 5} Y = {1, 2, 3}
The union of X and Y is the set which consists of all the elements of X and Y
X ∪ Y= {1, 2, 3, 5}
(ii) A = [ a, e, i, o, u} B = {a, b, c}
(ii) A = {a, e, i, o, u} B = {a, b, c}
The union of A and B is the set which consists of all the elements of A and B
A∪ B = {a, b, c, e, i, o, u}
(iii) A = {x : x is a natural number and multiple of 3}
B = {x : x is a natural number less than 6}
(iii) A = {x: x is a natural number and multiple of 3} = {3, 6, 9 …}
B = {x: x is a natural number less than 6} = {1, 2, 3, 4, 5, 6}
So the union of the pairs of set can be written as
A ∪ B = {1, 2, 4, 5, 3, 6, 9, 12 …}
Hence, A ∪ B = {x: x = 1, 2, 4, 5 or a multiple of 3}
(iv) A = {x : x is a natural number and 1 < x ≤6 }
B = {x : x is a natural number and 6 < x < 10 }
(iv) A = {x: x is a natural number and 1 < x ≤ 6} = {2, 3, 4, 5, 6}
B = {x: x is a natural number and 6 < x < 10} = {7, 8, 9}
The union of A and B is the set which consists of all the elements of A and B
A∪ B = {2, 3, 4, 5, 6, 7, 8, 9}
Hence, A∪ B = {x: x ∈ N and 1 < x < 10}
(v) A = {1, 2, 3}, B = φ
(v) A = {1, 2, 3}, B = Φ
The union of A and B is the set which consists of all the elements of A and B
A ∪ B = {1, 2, 3}
Question 2 Let A = { a, b }, B = {a, b, c}. Is A ⊂ B ? What is A ∪ B ?
Answer A = {a, b} and B = {a, b, c}
To find if A ⊂ B and A ∪ B
A set A is said to be a subset of B if every element of A is also an element of B
It can be observed that A⊂ B
A∪B = {a,b } ∪ {a,b,c}
∴A ∪ B = {a,b,c}
Question 3 If A and B are two sets such that A ⊂ B, then what is A ∪ B ?
Answer If A and B are two sets such that
A ⊂ B, then A ∪ B = B.
Question 4) If A = {1, 2, 3, 4}, B = {3, 4, 5, 6}, C = {5, 6, 7, 8 } , D = { 7, 8, 9, 10 }; find
(i) A ∪ B (ii) A ∪ C (iii) B ∪ C
(iv) B ∪ D (v) A ∪ B ∪ C (vi) A ∪ B ∪ D
(vii) B ∪ C ∪ D
Answer
(i) A ∪ B = {1, 2, 3, 4, 5, 6}
(ii) A ∪ C = {1, 2, 3, 4, 5, 6, 7, 8}
(iii) B ∪ C = {3, 4, 5, 6, 7, 8}
(iv) B ∪ D = {3, 4, 5, 6, 7, 8, 9, 10}
(v) A ∪ B ∪ C = {1, 2, 3, 4, 5, 6, 7, 8}
(vi) A ∪ B ∪ D = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
(vii) B ∪ C ∪ D = {3, 4, 5, 6, 7, 8, 9, 10}
Question 5 Find the intersection of each pair of sets of
(i) X = {1, 3, 5} Y = {1, 2, 3}
(i) X = {1, 3, 5}, Y = {1, 2, 3}
So the intersection of the given set can be written as
X ∩ Y = {1, 3}
(ii) A = {a, e, i, o, u} B = {a, b, c}
(ii) A = {a, e, i, o, u}, B = {a, b, c}
So the intersection of the given set can be written as
A ∩ B = {a}
(iii) A = {x: x is a natural number and multiple of 3}
B = {x: x is a natural number less than 6}
(iii) A = {x: x is a natural number and multiple of 3} = (3, 6, 9 …}
B = {x: x is a natural number less than 6} = {1, 2, 3, 4, 5}
So the intersection of the given set can be written as
A ∩ B = {3}
(iv) A = {x: x is a natural number and 1 < x ≤ 6}
B = {x: x is a natural number and 6 < x < 10}
(iv) A = {x: x is a natural number and 1 < x ≤ 6} = {2, 3, 4, 5, 6}
B = {x: x is a natural number and 6 < x < 10} = {7, 8, 9}
So the intersection of the given set can be written as
A ∩ B = Φ
(v) A = {1, 2, 3}, B = Φ
(v) A = {1, 2, 3}, B = Φ
So the intersection of the given set can be written as
A ∩ B = Φ
Question 6 If A = { 3, 5, 7, 9, 11 }, B = {7, 9, 11, 13}, C = {11, 13, 15} and D = {15, 17}; find
(i) A ∩ B (ii) B ∩ C (iii) A ∩ C ∩ D
(iv) A ∩ C (v) B ∩ D (vi) A ∩ (B ∪ C)
(vii) A ∩ D (viii) A ∩ (B ∪ D) (ix) ( A ∩ B ) ∩ ( B ∪ C )
(x) ( A ∪ D) ∩ ( B ∪ C)
Answer
(i) A ∩ B = {7, 9, 11}
(ii) B ∩ C = {11, 13}
(iii) A ∩ C ∩ D = {A ∩ C} ∩ D = {11} ∩ {15, 17} = Φ
(iv) A ∩ C = {11}
(v) B ∩ D = Φ
(vi) A ∩ (B ∪ C) = (A ∩ B) ∪ (A ∩ C) = {7, 9, 11} ∪ {11} = {7, 9, 11}
(vii) A ∩ D = Φ
(viii) A ∩ (B ∪ D) = (A ∩ B) ∪ (A ∩ D) = {7, 9, 11} ∪ Φ = {7, 9, 11}
(ix) (A ∩ B) ∩ (B ∪ C) = {7, 9, 11} ∩ {7, 9, 11, 13, 15} = {7, 9, 11}
(x) (A ∪ D) ∩ (B ∪ C) = {3, 5, 7, 9, 11, 15, 17) ∩ {7, 9, 11, 13, 15} = {7, 9, 11, 15}
Question 7 If A = {x : x is a natural number },
B = {x : x is an even natural number}
C = {x : x is an odd natural number} and
D = {x : x is a prime number }, find
(i) A ∩ B (ii) A ∩ C (iii) A ∩ D
(iv) B ∩ C (v) B ∩ D (vi) C ∩ D
Answer
A = {x: x is a natural number} = {1, 2, 3, 4, 5 …}
B ={x: x is an even natural number} = {2, 4, 6, 8 …}
C = {x: x is an odd natural number} = {1, 3, 5, 7, 9 …}
D = {x: x is a prime number} = {2, 3, 5, 7 …}
(i) A ∩B = {x: x is a even natural number} = B
(ii) A ∩ C = {x: x is an odd natural number} = C
(iii) A ∩ D = {x: x is a prime number} = D
(iv) B ∩ C = Φ
(v) B ∩ D = {2}
(vi) C ∩ D = {x: x is odd prime number}
Question 8 Which of the following pairs of sets are disjoint
(i) {1, 2, 3, 4} and {x : x is a natural number and 4 ≤ x ≤ 6 }
(i) {1, 2, 3, 4}
{x: x is a natural number and 4 ≤ x ≤ 6} = {4, 5, 6}
So we get
{1, 2, 3, 4} ∩ {4, 5, 6} = {4}
Hence, this pair of sets is not disjoint.
(ii) { a, e, i, o, u } and { c, d, e, f }
(ii) {a, e, i, o, u} ∩ (c, d, e, f} = {e}
Hence, {a, e, i, o, u} and (c, d, e, f} are not disjoint.
(iii) {x : x is an even integer } and {x : x is an odd integer}
(iii) {x: x is an even integer} ∩ {x: x is an odd integer} = Φ
Hence, this pair of sets is disjoint.
Question 9 If A = {3, 6, 9, 12, 15, 18, 21}, B = { 4, 8, 12, 16, 20 },
C = { 2, 4, 6, 8, 10, 12, 14, 16 }, D = {5, 10, 15, 20 }; find
(i) A – B
(i) A – B = {3, 6, 9, 15, 18, 21}
(ii) A – C
(ii) A – C = {3, 9, 15, 18, 21}
(iii) A – D
(iii) A – D = {3, 6, 9, 12, 18, 21}
(iv) B – A
(iv) B – A = {4, 8, 16, 20}
(v) C – A
(v) C – A = {2, 4, 8, 10, 14, 16}
(vi) D – A
(vi) D – A = {5, 10, 20}
(vii) B – C
(vii) B – C = {20}
(viii) B – D
(viii) B – D = {4, 8, 12, 16}
(ix) C – B
(ix) C – B = {2, 6, 10, 14}
(x) D – B
(x) D – B = {5, 10, 15}
(xi) C – D
(xi) C – D = {2, 4, 6, 8, 12, 14, 16}
(xii) D – C
(xii) D – C = {5, 15, 20}
Question 10 If X= { a, b, c, d } and Y = { f, b, d, g}, find
(i) X – Y
(i) X – Y = {a, c}
(ii) Y – X
(ii) Y – X = {f, g}
(iii) X ∩ Y
(iii) X ∩ Y = {b, d}
Question 11 If R is the set of real numbers and Q is the set of rational numbers, then what is R – Q?
Answer
R – Set of real numbers
Q – Set of rational numbers
Hence, R – Q is a set of irrational numbers.
Question 12 State whether each of the following statement is true or false. Justify your answer.
(i) { 2, 3, 4, 5 } and { 3, 6} are disjoint sets.
(i) False
If 3 ∈ {2, 3, 4, 5}, 3 ∈ {3, 6}
So we get {2, 3, 4, 5} ∩ {3, 6} = {3}
(ii) { a, e, i, o, u } and { a, b, c, d }are disjoint sets.
(ii) False
If a ∈ {a, e, i, o, u}, a ∈ {a, b, c, d}
So we get {a, e, i, o, u} ∩ {a, b, c, d} = {a}
(iii) { 2, 6, 10, 14 } and { 3, 7, 11, 15} are disjoint sets.
(iii) True
Here {2, 6, 10, 14} ∩ {3, 7, 11, 15} = Φ
(iv) { 2, 6, 10 } and { 3, 7, 11} are disjoint sets.
(iv) True
Here {2, 6, 10} ∩ {3, 7, 11} = Φ
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