Discrete Mathematics Interview Questions and Answers on “Set Operations”.
1. Let the set A is {1, 2, 3} and B is {2, 3, 4}. Then the number of elements in A U B is?
a) 4
b) 5
c) 6
d) 7
Answer: a
Clarification: AUB is {1, 2, 3, 4}.
2. Let the set A is {1, 2, 3} and B is { 2, 3, 4}. Then number of elements in A ∩ B is?
a) 1
b) 2
c) 3
d) 4
Answer: b
Clarification: A ∩ B is {2, 3}.
3. Let the set A is {1, 2, 3} and B is {2, 3, 4}. Then the set A – B is?
a) {1, -4}
b) {1, 2, 3}
c) {1}
d) {2, 3}
Answer: c
Clarification: In A – B the common elements get cancelled.
4. In which of the following sets A – B is equal to B – A?
a) A = {1, 2, 3}, B = {2, 3, 4}
b) A = {1, 2, 3}, B = {1, 2, 3, 4}
c) A = {1, 2, 3}, B = {2, 3, 1}
d) A = {1, 2, 3, 4, 5, 6}, B = {2, 3, 4, 5, 1}
Answer: c
Clarification: A- B= B-A = Empty set.
5. Let A be set of all prime numbers, B be the set of all even prime numbers, C be the set of all odd prime numbers, then which of the following is true?
a) A ≡ B U C
b) B is a singleton set.
c) A ≡ C U {2}
d) All of the mentioned
Answer: d
Clarification: 2 is the only even prime number.
6. If A has 4 elements B has 8 elements then the minimum and maximum number of elements in A U B are ____________
a) 4, 8
b) 8, 12
c) 4, 12
d) None of the mentioned
Answer: b
Clarification: Minimum would be when 4 elements are same as in 8, maximum would be when all are distinct.
7. If A is {{Φ}, {Φ, {Φ}}}, then the power set of A has how many element?
a) 2
b) 4
c) 6
d) 8
Answer: b
Clarification: The set A has got 2 elements so n(P(A))=4.
8. Two sets A and B contains a and b elements respectively. If power set of A contains 16 more elements than that of B, value of ‘b’ and ‘a’ are _______
a) 4, 5
b) 6, 7
c) 2, 3
d) None of the mentioned
Answer: a
Clarification: 32-16=16, hence a=5, b=4.
9. Let A be {1, 2, 3, 4}, U be set of all natural numbers, then U-A’(complement of A) is given by set.
a) {1, 2, 3, 4, 5, 6, ….}
b) {5, 6, 7, 8, 9, ……}
c) {1, 2, 3, 4}
d) All of the mentioned
Answer: c
Clarification: U – A’ ≡ A.
10. Which sets are not empty?
a) {x: x is a even prime greater than 3}
b) {x : x is a multiple of 2 and is odd}
c) {x: x is an even number and x+3 is even}
d) { x: x is a prime number less than 5 and is odd}
Answer: d
Clarification: Because the set is {3}.