Set Theory Model Questions Set 2 Practice Questions Answers Test with Solutions & More Shortcuts

Question : 11

Let S be a set of first ten natural numbers. What is the possible number of pairs (a, b) where a, b E S and a ≠ b such that the product ab (> 12) leaves remainder 4 when divided by 12 ?

a) 8

b) 6

c) 4

d) 10

Answer: (a)

Since numbers which and leave 4 as Remainder when devided by 12 are

16, 28, 40, 52, 64, 76, 88, 100 and 124

16 = 2 × 8, 8 × 2

28 = 4 × 7, 7 × 4

40 = 4 × 10, 10 × 4, 5 × 5, 8 × 5

All remaining numbers doesn't meet the requirement

Answer is 8.

Question : 12

If two sets A and B have 2n and 4n elements, respectively. When n is a natural number. What can be the minimum number of elements in A ∪ B?

a) 4n

b) 3n

c) 2n

d) 6n

Answer: (a)

Here, n(A ∩ B) = 2n

∴ n(A ∪ B) = n(A) + n(B) – n(A ∩ B)

= 2n + 4n – 2n = 4n

Hence, minimum number of elements of A ∪ B is 4n.

Question : 13

If A and B are any two non-empty subsets of a set E, then what is A ∪ (A ∩ B) equal to?

a) A

b) A ∪ B

c) A ∩ B

d) B

Answer: (a)

A and B are non-empty subsets of E.

set-theory-aptitude-mcq

∴ A ∪ (A ∩ B) = A ∪ (Shaded portion) = A

Question : 14

If a set A contains 60 elements and another set B contains 70 elements and there are 50 elements in common, then how many elements does A ∪ B contain?

a) 80

b) 100

c) 130

d) 70

Answer: (a)

Here, n(A) = 60, n(B) = 70, n(A ∩ B) = 50 and n(A ∪ B) = ?

We know that:

n(A ∪ B) = n(A) + n(B) – n(A ∩ B)

= 60 + 70 – 50 = 130 – 50 = 80

Question : 15

Which one of the following is a null set?

a) C = {Φ}

b) B = {x : x + 3 = 3}

c) A = {x is a real number : x > 1 and x < 1}

d) D = {x is a real number : x ≥ 1 and x ≤ 1}

Answer: (c)

From option (a),

A = {x is a real number : x > 1 and x < 1}.

So, there is no element which is greater or less than 1.

So, A is a null set.

From option (b),

B = {x : x + 3 = 3} = {0}

= Singleton set

From option (c):

C = {Φ} = Singleton set

From option (d),

D = {x is a real number : x ≥ 1 and x ≤ 1}

= {1} = Singleton set

IMPORTANT quantitative aptitude EXERCISES

Set Theory Model Questions Set 2 Online Quiz

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