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

Question : 6

The set of natural numbers is closed under
I. addition
II. subtraction
III. multiplication
IV. division
Which of the above is/are correct?

a) I, II and III

b) Both I and III

c) Only I

d) Both III and IV

Answer: (b)

Set of natural numbers,

N = {1, 2, 3, 4, 5, 6, ...

(i) Addition: 2 + 3 = 5 is also an element of N.

(ii) Subtraction: 2 – 3 = –1 ∉ N

(iii) Multiplication: 2 × 3 = 6 ε N

(iv) Division: $3/2$. = 1.5 ∉ N (since, N contains only positive integers)

Therefore, the set of natural numbers is closed under addition and multiplication.

Question : 7

Consider the following in respect of the sets A and B.
I. (A ∩ B) ⊆ A
II. (A ∩ B) ⊆ B
III. A ⊆ (A ∪ B)
Which of the above are correct?

a) I and III

b) II and III

c) I and II

d) I, II and III

Answer: (d)

From figure,

set-theory-aptitude-mcq

(A ∩ B) ⊆ A (true)

(A ∩ B) ⊆ B (true)

and A ⊆ (A ∪ B) also (true)

Thus, all three statements are correct.

Shaded region = (A ∪ B).

Question : 8

A is a set of positive integers such that when divided by 2, 3, 4, 5 and 6 leaves the remainder 1, 2, 3, 4 and 5 respectively. How many integers between 0 and 100 belong to the set A ?

a) Two

b) One

c) No integer

d) Three

Answer: (b)

LCM of 2, 3, 4, 5, 6 = 60

Number when divided by 2, 3, 4, 5, 6 gives

remainder 1, 2, 3, 4, 5 respectively here 2 – 1 = 1

3 – 2 = 1, 4 – 3, = 1, 5 – 4 = 1, 6 – 5 = 1

So required no. = 60 – 1 = 59

other no. 59 × 2 = 118

i.e. there is one no. below 100.

Question : 9

Which one of the following is a correct statement?

a) Φ = P(Φ)

b) Φ ∉ P (Φ)

c) Φ ε Φ

d) Φ ε P(Φ)

Answer: (d)

In the given options, the correct statement is Φ ε P(Φ).

Question : 10

Which one of the following is an infinite set?

a) {x : x is a positive integer less than or equal to 1000}

b) {x : x is a natural number less than 1000}

c) {x : x is a whole number less than or equal to 1000}

d) {x : x is an integer and less than 1000}

Answer: (d)

In a given option only,

{x : x is an integer and less than 1000}

i.e., x ε (– ∞, 1000) is an infinite set.

IMPORTANT quantitative aptitude EXERCISES

Set Theory Model Questions Set 2 Online Quiz

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