Chapter:

70+ Unit 2 Solved MCQs

in Discrete Structure (DS)

Chapters

Chapter: Unit 2
1.

Define f(n) = n/2 + 1−(−1)n/4 for all n 2 Z. Thus, f: Z → Z, Z the set of all integers.Which is correct?

A. f is a function and is onto but not one-to-one.
B. f is a function and is onto and one-to- one.
C. f is a function and is not onto but is one-to-one.
D. f is a function and is not onto and not one-to-one
Answer» A. f is a function and is onto but not one-to-one.
2.

If f (x) = cos x and g(x) = x3 , then (f o g) (x) is

A. (cos x)3
B. cos 3 x
C. X (cos x )3
D. cos x3
Answer» D. cos x3
3.

Transitivity and irreflexive imply:

A. Symmetric
B. Reflexive
C. Irreflexive
D. Asymmetric
Answer» D. Asymmetric
4.

If R is a relation “Less Than” from A = {1,2,3,4} to B = {1,3,5} then RoR-1 is

A. {(3,3), (3,4), (3,5)}
B. {(3,1), (5,1), (3,2), (5,2), (5,3), (5,4)}
C. {(3,3), (3,5), (5,3), (5,5)}
D. {(1,3), (1,5), (2,3), (2,5), (3,5), (4,5)}
Answer» C. {(3,3), (3,5), (5,3), (5,5)}
5.

A relation that is reflexive, anti-symmetric and transitive is a

A. Function
B. equivalence relation
C. partial order
D. None of these
Answer» C. partial order
6.

Let f : X →Y and g : Y → Z. Let h = go f : X → Z. Suppose g is one-to-one and onto. Which of the following is FALSE?

A. If f is one-to-one then h is one-to- one and onto.
B. If f is not onto then h is not onto.
C. If f is not one-to- one then h is not one-to-one.
D. If f is one-to-one then h is one-to- one.
Answer» A. If f is one-to-one then h is one-to- one and onto.
7.

Domain and Range of the function Y = –v(–2x + 3) is

A. x=3/2, y=0
B. x>3/2, y=0
C. x<3/2, y=0
D. x=3/2, y=0
Answer» D. x=3/2, y=0
8.

The relation { (1,2), (1,3), (3,1), (1,1), (3,3), (3,2), (1,4), (4,2), (3,4)} is

A. Reflexive
B. Transitive
C. Symmetric
D. Asymmetric
Answer» B. Transitive
9.

A partial ordered relation is transitive, reflexive and

A. Anti-symmetric
B. Bisymmetric
C. Anti-reflexive.
D. Asymmetric
Answer» A. Anti-symmetric
10.

Find the number of relations from A = {cat, dog, rat} to B = {male , female}

A. 64
B. 6
C. 32
D. 15
Answer» A. 64
11.

The number of distinct relations on a set of 3 elements is

A. 8
B. 9
C. 18
D. 512
Answer» C. 18
12.

How many onto (or surjective) functions are there from an n-element (n => 2) set to a 2-element set?

A. 2n
B. 2n - 1
C. 2n - 2
D. 2(2n – 2)
Answer» C. 2n - 2
13.

How many relations are there on a set with n elements that are symmetric and a set with n elements that are reflexive and symmetric?

A. 2n(n+1)/2 and 2n.3n(n–1)/2
B. 3n(n–1)/2 and 2n(n–1)
C. 2n(n+1)/2 and 3n(n–1)/2
D. 2n(n+1)/2 and 2n(n–1)/2
Answer» D. 2n(n+1)/2 and 2n(n–1)/2
14.

The number of functions from an m element set to an n element set is:

A. mn
B. m+n
C. nm
D. m*n
Answer» A. mn
15.

Let R = {(a, a), (a, b)} be a relation on S = {a, b, c}. Then R is not reflexive and not symmetric.

A. T
B. F
Answer» A. T
16.

Let R = {(a, a), (a, b)} be a relation on S = {a, b, c}. Then R is not transitive.

A. T
B. F
Answer» B. F
17.

The function f : Z → Z given by f (x)= x +1 is a bijection.

A. T
B. F
Answer» A. T
18.

The function f : A → B is injective if whenever f (x)= f (y), where x, y € A, then x = y.

A. T
B. F
Answer» A. T
19.

Let A be a finite set. If f : A → A is injective then it is surjective.

A. T
B. F
Answer» A. T
20.

The union of two equivalence relations on a non- empty set is an equivalence relation.

A. T
B. F
Answer» B. F
21.

If A is a set with 3 elements, how many equivalence relations are there on A? Hint: The set of equivalence classes for a given equivalence relation on A is a partition of the set A.

A. 4
B. 5
C. 23
D. 29
Answer» B. 5
22.

Let f: A → B and g: B→C be functions where A = {1, 2, 3, 4}, B = {1, 2, 3, 4, 5}, and C = {1, 2, 3, 4, 5, 6}, f =
{(1, 2), (2, 3), (3, 2), (4, 5)} and g = {(1, 3), (2, 4), (3,
5), (4, 6), (5, 1)}. Find g o.f (2).

A. 3
B. 4
C. 5
D. 6
Answer» D. 6
23.

A relation R is defined on Z by xRy if 2x +5y = 0(mod7). Then the equivalence class[10] is equal to the equivalence class…

A. 3
B. 4
C. 5
D. 6
Answer» A. 3
24.

Let R be a relation on a set A = {1, 2, 3, 4} given by R =
{(1, 1), (1, 2), (1, 3), (2, 1), (2,2), (2, 3), (3, 1), (3, 2), (3,
3)}. Then the relation is:

A. reflexive and symmetric, but not transitive.
B. reflexive and transitive, but not symmetric.
C. symmetric and transitive, but not reflexive.
D. reflexive, but neither symmetric nor transitive.
Answer» C. symmetric and transitive, but not reflexive.
25.

If f (x) = -3x - 5, what is the value of f (2)?

A. -11
B. -1
C. 1
D. 11
Answer» A. -11
26.

If g (x) = 3x² - 2x - 5, what is the value of g (-1)?

A. -4
B. -10
C. 6
D. 0
Answer» A. -4
27.

Which relation is not a function?

A. {(2,5), (3,6), (4,7), (5,8)}
B. {(6,-2), (-4,6), (- 2,4), (1,0)}
C. {(-1, 5), (-2,5), (- 3,5), (-4,5)}
D. {(0,-2), (1,0), (-1,- 3), (0,-1)}
Answer» D. {(0,-2), (1,0), (-1,- 3), (0,-1)}
28.

Consider the recurrence relation ak = -8ak-1 - 15ak-2 with initial conditions a0 = 0 and a1 = 2. Which of the following is an explicit solution to this recurrence relation?

A. ak = (-3)k - (-5)k
B. ak = k(-3)k - k(- 5)k
C. ak = k(-3)k - (-5)k
D. ak = (-5)k - (-3)k
Answer» A. ak = (-3)k - (-5)k
29.

Consider the recurrence relation ak = 6ak-1 - 9ak-2 with initial conditions a0 = 0 and a1 = 2. Which of the following is an explicit solution to this recurrence relation, provided the constants A and B are chosen correctly?

A. an = A3n + B3n
B. an = A3n + B(-3)n
C. an = A3n + nB3n
D. an = A(-3)n + nB(- 3)n
Answer» C. an = A3n + nB3n
30.

The binary relation R = {(0, 0), (1, 1)} on A = {0, 1, 2, 3, } is

A. Reflexive, Not Symmetric, Transitive
B. Not Reflexive, Symmetric, Transitive
C. Reflexive, Symmetric, Not Transitive
D. Reflexive, Not Symmetric, Not Transitive
Answer» B. Not Reflexive, Symmetric, Transitive
31.

Define a binary relation R = {(0, 1), (1, 2), (2, 3), (3, 2), (2, 0)} on A = {0, 1, 2, 3}. The directed graph (including loops) of the transitive closure of this relation has

A. 16 arrows
B. 12 arrows
C. 8 arrows
D. 6 arrows
Answer» A. 16 arrows
32.

Let N+ denote the nonzero natural numbers. Define a binary relation R on N+ × N+ by (m, n)R(s, t) if gcd(m, n) = gcd(s, t). The binary relation R is

A. Reflexive, Not Symmetric, Transitive
B. Not Reflexive, Symmetric, Transitive
C. Reflexive, Symmetric, Not Transitive
D. Reflexive, Not Symmetric, Not Transitive
Answer» A. Reflexive, Not Symmetric, Transitive
33.

Define a binary relation R on a set A to be anti- reflexive if xRx doesn’t hold for any x 2 A. The number of symmetric, anti-reflexive binary relations on a set of ten elements is

A. 210
B. 250
C. 245
D. 290
Answer» C. 245
34.

Define an equivalence relation R on the positive integers A = {2, 3, 4, . . . , 20} by m R n if the largest prime divisor of m is the same as the largest prime divisor of n. The number of equivalence classes of R is

A. 8
B. 10
C. 9
D. 11
Answer» A. 8
35.

Consider the divides relation, m | n, on the set A = {2, 3, 4, 5, 6, 7, 8, 9, 10}. The cardinality of the covering relation for this partial order relation (i.e., the number of edges in the Hasse diagram) is

A. 6
B. 5
C. 8
D. 7
Answer» D. 7
36.

Let A = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16} and consider the divides relation on A. Let C denote the length of the maximal chain, M the number of maximal elements, and m the number of minimal elements. Which is true?

A. C = 3, M = 8, m = 6
B. C = 4, M = 8, m = 6
C. C = 3, M = 6, m = 6
D. C = 4, M = 6, m = 4
Answer» A. C = 3, M = 8, m = 6
37.

Consider the binary relation R = {(x,y), (x,z), (z,x), (z,y)} on the set {x,y,z}. Which one of the following is TRUE?

A. R is symmetric but NOT antisymmetric
B. R is NOT symmetric but antisymmetric
C. R is both symmetric and antisymmetric
D. R is neither symmetric nor antisymmetric
Answer» D. R is neither symmetric nor antisymmetric
38.

Let S be a set of n elements. The number of ordered pairs in the largest and the smallest equivalence relations on S are:

A. n and n
B. 2 n and n
C. 2 n and 0
D. n and 1
Answer» A. n and n
39.

Which one of the following is the example of nonlinear data structure?

A. Graph
B. Binary Tree
C. Queue
D. Link List
Answer» A. Graph
40.

If |A|=5 and |B|=4, then there exists an injective function f: B→A.

A. T
B. F
Answer» B. F
41.

The set of even integers is well-ordered.

A. T
B. F
Answer» B. F
42.

If n is an integer and x is an irrational real number, then nx is irrational.

A. T
B. F
Answer» B. F
43.

In Z7, if [6]x =[3]then x =? .

A. [1]
B. [2]
C. [3]
D. [4]
Answer» D. [4]
44.

Which statement represents "all numbers between negative 4 and positive 8" ?

A. -4 > x > 8
B. -4 < x < 8
C. -4 > x < 8
D. None of these
Answer» B. -4 < x < 8
45.

Which interval notation represents the set of numbers that are greater than or equal to -1, but are less than 9?

A. (-1,9]
B. [-1,9]
C. (-1,9)
D. [-1,9)
Answer» D. [-1,9)
46.

Given the relation D = {(6,4), (8,-1), (x,7), (-3,-6)}. Which of the following values for x will make relation D a function?

A. -3
B. -6
C. 8
D. 6
Answer» A. -3
47.

Which statement is true about the relation shown at the right?

A. It is a function because there exists one y- coordinate for each x- coordinate.
B. It is a function because there exists one x- coordinate for each y-coordinate.
C. It is not a function because there are multiple x-values for a given y-value.
D. It is not a function because there are multiple y-values for a given x- value.
Answer» C. It is not a function because there are multiple x-values for a given y-value.
48.

A ball is tossed in the air in such a way that the path of the ball is modeled by the equation y = -x² + 6x, where y represents the height of the ball in feet and x is the time in seconds. At what time, x, is the ball at its highest point?

A. 6
B. 2
C. 3
D. 4
Answer» B. 2
49.

Let S = {1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21}. What is the
smallest integer N > 0 such
that for any set of N integers, chosen from S, there must be two distinct integers that
divide each other? IZ

A. 10
B. 7
C. 9
D. 8
Answer» D. 8
50.

If S is a set containing n elements then number of elements in power set of S ,i.e.P(S)    

A. n
B. 2n
C. 2n
D. n2
Answer» C. 2n
51.

If A and B are two non empty sets then cartesian product of A and B is----------

A. AΧB={(a,b);a,bϵA }
B. AΧB={(a,b);a,bϵB}
C. AΧB={(a,b);aϵA and bϵB}
D. AΧB={(a,b);aϵB and bϵA}
Answer» C. AΧB={(a,b);aϵA and bϵB}
52.

If set A contains n elements, set B contains m elements then number of elements in AXB is---

A. m+n
B. n-m
C. m.n
D. n/m
Answer» C. m.n
53.

If A,B and C are non empty sets then AX(B∩C) is-----.

A. (AXB)U(AXC)
B. (AXB)∩(AXC)
C. (AXB)∩C
D. (AXC)∩B
Answer» B. (AXB)∩(AXC)
54.

If A,B and C are non empty sets then AX(BUC) is-----.

A. (AXB)U(AXC)
B. (AXB)∩(AXC)
C. (AXB)UC
D. (AXC)UB
Answer» A. (AXB)U(AXC)
55.

If R is a relation defined from set A to set B then------

A. R=AXB
B. RCAXB
C. RCBXA
D. AXBCR
Answer» B. RCAXB
56.

If A=(1,2,3} and R on A is defined by R={(1,1),(2,2),(3,3)} then R is…………

A. Reflexive
B. Symmetric
C. Transitive
D. All of these
Answer» A. Reflexive
57.

If A=(1,2,3} and R on A is defined by R={(1,2),(2,1),(1,1),(2,2)} then R is…………

A. Reflexive and symmetric
B. Reflexive and Transitive
C. Symmetric and Transitive
D. All of the above.
Answer» C. Symmetric and Transitive
58.

Which statement is true?

A. Relation can be of the type one many
B. Function can be of the type one many
C. Both (a) and (b)
D. None of these.
Answer» B. Function can be of the type one many
59.

Which statement is true?

A. Every function is a relation.
B. Every Relation is a function.
C. Both A and B.
D. None of these.
Answer» A. Every function is a relation.
60.

In-----Relation every element is related with itself.

A. Reflexive
B. Symmetric
C. Transitive
D. None
Answer» A. Reflexive
61.

The Relation is----------if a has relation with b and b has relation with a.

A. Reflexive
B. Symmetric
C. Transitive
D. None
Answer» B. Symmetric
62.

If a has relation with b and b has relation with c then a has relation with c is………………..Relation.

A. Reflexive
B. Symmetric
C. Transitive
D. None
Answer» C. Transitive
63.

Types of function Mappings are-----

A. One to one
B. Many to one
C. Into, Onto
D. All
Answer» D. All
64.

The Transitive Closure of a relation R is denoted by----

A. R*
B. R    
C. R+
D. RR
Answer» A. R*
65.

The alternative method to find transitive closure of R* is-------.

A. R*
B. RR
C. Warshall’s Algorithm
D. R
Answer» C. Warshall’s Algorithm
66.

Poset is a------

A. Positive set
B. p-set
C. P*
D. Partially Ordered set
Answer» D. Partially Ordered set
67.

If A is any non-empty set and R is a partial ordered relation on set A, then the ordered pair (A,R) is called -------

A. Poset
B. p-set
C. Positive set
D. None
Answer» A. Poset
68.

Let (A, ≤) be a poset. A subset of A is known as ------if every pair of elements in the subset are related.

A. Chain
B. Antichains
C. Group
D. Lattice.
Answer» A. Chain
69.

The number of elements in the chain is called as------

A. Chain
B. Antichains
C. None
D. Length of chain
Answer» D. Length of chain
70.

A ------ is a poset (A, ≤) in which every subset {a, b} of A, has a least upper bound and a greatest lower bound.

A. Chain
B. Lattice.
C. Antichains
D. Group
Answer» B. Lattice.
71.

Pigeon Hole Principle says that if there are many pigeons and a few pigeon holes, then there must be some pigeon holes occupied by--------------

A. Two or more pigeons.
B. Pigeons
C. One only
D. None
Answer» A. Two or more pigeons.
72.

Digraph can be represented by-----

A. Hasse diagrams
B. Digraph
C. Graph
D. None
Answer» A. Hasse diagrams
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