Page 11 - Mathematics Class - XI

Viva-Voce

1. What is an empty set?
Ans. A set is said to be an empty set if it has no element and it is denoted by φ.
2. What is singleton set? Give an example also.
Ans. A set is said to be singleton set if it has only one element. For example, {2} is a singleton set.
3. Write all the subsets of set A = {1, 2}.

Ans. The subsets of set A are φ, {1}, {2}, {1, 2}.
4. If A = {x ∈ Z: x = (–1) , where n ∈ N}, write all the possible subsets of A.
n
Ans. A = {1, –1}, subsets of A are φ ,{1}, {–1}, {1, –1}.
5. Write all the subsets of set A = {1, 2, 3}.
Ans. The number of subsets of set A are φ, {1}, {2}, {3}, {1, 2}, {2, 3}, {3, 1}, {1, 2, 3}.
6. What are the other names of an empty set?
Ans. Null set or void set.

MCQs

1. The set of natural numbers represented by the symbol

a) Q b) N c) I d) None of these
+
2. If A {x : 3x – 12x = 0, x is a natural number}, then set equal to
2
a) {0, 4} b) {4} c) {φ} d) {1, 2, 3 ........ }
3. Which of the following set is a null set or void set?

a) {x : x + y = 6} b) {x : x – 6x + 9 = 0}
2
c) {x : x = x } d) {x : x < x}
2
4. Two finite sets have p and q elements. The total number of subsets of the first set is 112 more then the total
number of subsets of the second set. The values of p and q are

a) 4, 7 b) 7, 4 c) 4, 4 d) 7, 7
5. The number of subsets from the word ‘FOLLOW’
a) 16 b) 64 c) 15 d) 32

6. The number of proper subsets from the letter of word ‘ALLAHABAD’.
a) 512 b) 256 c) 32 d) 31
7. Find the number of subsets of set A = {2, 4, 5}

a) 8 b) 16 c) 24 d) 7

Answers: 1. b) N 2. c) {φ} 3. d) {x : x < x}
4. b) 64 5. a) 16 6. d) 31 7. a) 8

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