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All questions of Sets for Commerce Exam

 The Shaded region in the following figure illustrates
  • a)
    A ∩ ( B ∪ C)
  • b)
    A ∩ B ∩ C
  • c)
    A ∪ B ∪ C
  • d)
    (A ∩ B) ∪ (A ∩ C)
Correct answer is option 'D'. Can you explain this answer?

New Words answered
First which region is over which region Then We will see that A is on the B so A intersection B and after C is on the A so, A intersection C after that we have to take all intersection part so A intersection B is Union with A intersection C.
The shaded region represents (A ∩ B) ∪ (A ∩ C).

If A = {a, b, c} then the number of proper subsets of A are:
  • a)
    3
  • b)
    10
  • c)
    7
  • d)
    8
Correct answer is option 'C'. Can you explain this answer?

Pooja Nair answered
  • Number of proper subsets of a given set = 2m - 1, where m is the number of elements.
  • Here the number of elements is 3. So the number of proper subsets of A = 23 - 1 = 7.

Can you explain the answer of this question below:

If A = {5, 10, 15}, B = ϕ, then B – A is

  • A:

    5

  • B:

    {5,10}

  • C:

    ϕ

  • D:

    {5,10, 15}

The answer is c.

Om Desai answered
If A = {5, 10, 15}, B = ϕ
B - A will have those elements which are in B but not in A.
B - A = ϕ

 Which of the following is not an empty set?
  • a)
    {x : x is a multiple of 7, x < 7, x ∈ N}
  • b)
    Set of common points of two parallel lines in a plane
  • c)
    {x : 6 + 2x > 5x + 3, x ∈ N}
  • d)
    Set of smallest whole number
Correct answer is option 'D'. Can you explain this answer?

Ayush Joshi answered
As, the set of Whole numbers is {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ...};
So, according to the set of whole numbers above, the smallest whole number should be "0" and therefore the set of smallest whole number is not empty.

The set A = {1,4,9,16,25—} in set builder form is written as
  • a)
    A = {x:x is a prime number}
  • b)
    A ={x:x is the cube of a natural number}
  • c)
    A = {x:x is the square of a natural number}
  • d)
    A = {x:x is an even natural number}
Correct answer is 'C'. Can you explain this answer?

Krishna Iyer answered
  • We know that, 12 = 1, 22 = 4, 32 = 9, 42 = 16, 52 = 25
  • Therefore the set A = {1, 4, 9, 16, 25...} can be written in set builder form as: 
    A = {x: x is the square of a natural number}

 If ordered pair (a + 2b, 9) = (7, 3a + 2b), then the values of a and b are
  • a)
    9, 7
  • b)
    1, 3
  • c)
    7, 9
  • d)
    3, 1
Correct answer is option 'B'. Can you explain this answer?

A+2B=7------(1)
3A+2B=9------(2)
Subtracting (2) from (1)
we get, 2A=2
A=1
Subsitute A=1 in (1)
1+2B=7
2B=6
B=3
therefore A = 1, B = 3
 

For the set of all natural numbers the universal set can be
  • a)
    Set of all odd numbers
  • b)
    Set of all even numbers
  • c)
    Set of all integers
  • d)
    Set of all prime numbers
Correct answer is option 'C'. Can you explain this answer?

Krishna Iyer answered
Integers contain all the natural numbers. So it can be a universal set for natural numbers. In other options, there are only some of the elements of natural numbers.

 Choose the incorrect statement
  • a)
    If a set has only one element, we call it a singleton set.
  • b)
    Set of all even prime numbers is a subset of set of all natural numbers.
  • c)
    Φ is not a subset of any set.
  • d)
    Every set is a subset of itself.
Correct answer is option 'C'. Can you explain this answer?

Rohit Joshi answered
set A is a proper subset of a set B if A is a subset of B and there is at least one element of B that's not an element of A. Thus, the void set is a subset of all sets, and it's a proper subset of every set except itself

 If U= set of all whole numbers less than 12, A=set of all whole numbers less than 10, B= Set of all odd natural numbers less than 10, then what is (A∩B)’?
  • a)
    {3,5,7,9}
  • b)
    {0,1,3,5,7,9}
  • c)
    {0,2,4,6,8,10,11}
  • d)
    {1,3,5,7}
Correct answer is option 'A'. Can you explain this answer?

Hansa Sharma answered
U = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}
A = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
B = {1, 3, 5, 7, 9}
A ∩ B = {1, 3, 5, 7, 9}
(A ∩ B)’ = U - (A ∩ B)
(A ∩ B)’ = {0, 2, 4, 6, 8, 10, 11}

If Q = {x : x = 1/y , where y ∈ N} , then
  • a)
    1 ∈ Q
  • b)
    0 ∈ Q
  • c)
    1/2 ∈ Q
  • d)
    2 ∈ Q
Correct answer is option 'B'. Can you explain this answer?

Pooja Shah answered
We know that
n(A∪B)=n(A)+n(B)−n(A∩B)......(i)
n(A∪B)=n(A)+n(B)-n(A∩B)......(i)
Case 1 From (i) , it is clear that n(A∪B)
n(A∪B) will be maximum when n(A∩B)=0
In that case, 
n(A∪B)=n(A)+n(B)=(3+6)=9
∴ Maximum number of elements in 
(A∪B)=9
Case 2 From (i) , it is clear that n(A∪B)
n(A∪B) will be minimum when n(A∩B)=0 maximum ,i.e, when 
n(A∩B)=3
In this case, 
n(A∪B)=n(A)+n(B)−n(A∩B)=(3+6−3)=6
∴ minimum number of elements in 
A∪B=6

From the sets given below, select equal sets :
A = { 2, 4, 8, 12}, B = { 1, 2, 3, 4},
C = { 4, 8, 12, 14}, D = { 3, 1, 4, 2}
  • a)
    A and C
  • b)
    A and B
  • c)
    B and D
  • d)
    B and C
Correct answer is option 'C'. Can you explain this answer?

Mansi Chopra answered
 The sets are equal, if they have the exact same elements in them. Since option B & D have exactly same number of elements in them So, B & D are equal sets. 

Consider the set A of all divisors of 30. How many subsets of A contains even divisors only?
  • a)
    2
  • b)
    16
  • c)
    28
  • d)
    4
Correct answer is 'B'. Can you explain this answer?

Himaja Ammu answered
Set of divisors of 30={1,2,3,6,10,15,30} in these the even divisors r={2,6,10,30} we know no.of subsets to any set=2^n so answer is 2^4=16

 The number of elements in the Power set P(S) of the set S = [ [ Φ] , 1, [ 2, 3 ]] is
  • a)
    2
  • b)
    4
  • c)
    8
  • d)
    None of these
Correct answer is option 'C'. Can you explain this answer?

Preeti Iyer answered
There’s a result in mathematics used for this. It says that a power set B of any set A is a set of all the subsets of A and the number of elements of B will be 2^n where n is the number of elements of A.
So taking your question as an example;
A = {1,2,3}
B : set of all subsets of A
List out all the subsets of A - {1},{2},{3},{1,2},{2,3},{1,3},{1,2,3},{empty set}
Number of elements in A (n) = 3 
so 23 = 8
So, B = {{1},{2},{3},{1,2},{2,3},{1,3},{1,2,3},{empty set}} 
and the number of elements are 8.

Let U = {1,2,3,4,5,6,7,8,9,10} , A = {1,2,5} , B = {6,7}. Then A∩B’ is :
  • a)
    A
  • b)
    B
  • c)
    B’
  • d)
    none
Correct answer is option 'A'. Can you explain this answer?

Pooja Shah answered
  • B' gives us all the elements in U other than 6 and 7 i.e., B' = {1, 2, 3, 4, 5, 8, 9, 10}
  • The intersection of this set with A will be the common elements in both of these (A and B') i.e., = {1, 2, 5} which is set A itself.

Which of the following has only one subset?
  • a)
    { }
  • b)
    {5}
  • c)
    {4,5}
  • d)
    {0}
Correct answer is option 'A'. Can you explain this answer?

Vijay Kumar answered
  • Every set has the empty set as a subset. So if a set has 1 element, like {0}, then it will have 2 subsets: itself and the empty set, which is denoted by { }.
  • So, if a set has only one subset, then this set must be the empty set.

If n (P) = 5, n(Q) = 12 and n(P U Q) = 14 then n(P ∩ Q) =
  • a)
    3
  • b)
    4
  • c)
    5
  • d)
    7
Correct answer is option 'A'. Can you explain this answer?

Hansa Sharma answered
n (P) = 5, n(Q) = 12 and n(PUQ) = 14
n(PUQ) = n(P) + n(Q) - n(P∩Q) 
14 = 5 + 12 - n(P∩Q)
n(P∩Q) = 3

If A = {1, 2, 3, 4}, B = {3, 4} and C = {2, 3} then n ((A ∩ B x C)
  • a)
    2
  • b)
    8
  • c)
    4
  • d)
    16
Correct answer is option 'C'. Can you explain this answer?

Gaurav Kumar answered
A = {1, 2, 3, 4}, B = {3, 4} and C = {2, 3} 
(A ∩ B) = {3, 4} C = {2, 3}
(A ∩ B x C) = {3,4} x {2,3}
⇒ {(3,2) (3,3) (4,2) (4,3)}

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