Topic Question Set


Q 11 :

Let A = {1, 2, 3, ..., 100} and R be a relation on A such that R = {(a, b) : a = 2b + 1}. Let (a1,a2),(a2,a3),(a3,a4),...,(ak,ak+1) be a sequence of k elements of R such that the second entry of an ordered pair is equal to the first entry of the next ordered pair. Then the largest integer k, for which such a sequence exists, is equal to :          [2025]

  • 8

     

  • 5

     

  • 6

     

  • 7

     

(2)

Let the smallest value is ak+1 in A = {1, 2, 3, ..., 100}.

Since, ak=2ak+1+1=(2×1)+1=3

       ak1=2ak+1=(2×3)+1=7

           ak2=2ak1+1=(2×7)+1=15

          ak3=2ak2+1=(2×15)+1=31

          ak4=2ak3+1=(2×31)+1=63

          ak5=2ak4+1=(2×63)+1=127A

   The sequence is {(63, 31), (31, 15), (15, 7), (7, 3), (3, 1)}

   k = 5



Q 12 :

Let A = {–3, –2, –1, 0, 1, 2, 3}. Let R be a relation on A defined by xRy if and only if 0<x2+2y4. Let l be the number of elements in R and m be the minimum number of elements required to be added in R to make it reflexive relation. Then l + m is equal to          [2025]

  • 18

     

  • 20

     

  • 17

     

  • 19

     

(1)

A = {–3, –2, –1, 0, 1, 2, 3}

xRy if and only if 2yx242y

y = –3          6x210                x{3,3}

y = –2          4x28                  x{2,2}

y = –1          2x26                  x{2,2}

y = 0            0x24                  x{2,1,0,1,2}

y = 1            2x22               x{1,0,1}

y = 2            4x20               x{0}

y = 3            6x22            Value of x does not exist

R = {(–3, –3), (3, –3), (–2, –2),(2, –2), (–2, –1), (2, –1), (–2, 0), (–1, 0), (0,0), (1, 0), (2, 0), (–1, 1), (0, 1), (1, 1), (0, 2)}

   l = 15

To make it reflexive we will add (–1, –1), (2, 2), (3, 3) in R

   l + m = 15 + 3 = 18.



Q 13 :

Let A = {–2, –1, 0, 1, 2, 3}. Let R be a relation on A defined by xRy if and only if y = max{x, 1}. Let l be the number of elements in R. Let m and n be the minimum number of elements required to be added in R to make it reflexive and symmetric relations, respectively. Then l + m + n is equal to          [2025]

  • 13

     

  • 12

     

  • 14

     

  • 11

     

(2)

We have, A = {–2, –1, 0, 1, 2, 3} and

R = {(–2, 1), (—1, 1), (0, 1), (1, 1), (2, 2), (3, 3)}.

Now, number of elements in R i.e., l = 6

For R to be reflexive,

R = {(–2, –2), (–1, –1), (0, 0), (–2, 1), (–1, 1), (0, 1), (1, 1), (2, 2), (3, 3)}

So, we need to add three elements to make it reflexive.

   m = 3

For R to be symmetric,

R = {(–2, 1), (1, –2), (–1, 1), (1, –1), (0, 1), (1, 0), (1, 1), (2, 2), (3, 3)}

So, we need to add three elements to make it symmetric.

   n = 3

So, l + m + n = 6 + 3 + 3 = 12.



Q 14 :

Let A = {–3, –2, –1, 0, 1, 2, 3} and R be a relation on A defined by xRy if and only if 2xy  {0, 1}. Let l be the number of elements in R. Let m and n be the minimum number of elements required to be added in R to make it reflexive and symmetric relations, respectively. Then l + m + n is equal to :          [2025]

  • 17

     

  • 16

     

  • 18

     

  • 15

     

(1)

We have, A = {–3, –2, –1, 0, 1, 2, 3}, R is defined on A as xRy such that 2xy  {0, 1}.

i.e., 2xy = 0 or 2xy = 1

   R = {(0, 0), (–1, –2), (1, 2), (0, –1), (2,3), (1, 1), (–1, –3)} i.e., l = 7

For R to be reflexive, i.e., we need 5 more elements {(2, 2), (–1, –1), (3, 3), (–3, –3), (–2, –2)} so m = 5 and for R to be symmetric, we need 5 more elements {(–2, –1), (2, 1), (–1, 0), (3, 2), (–3, –1)}, so n = 5.

   l + m + n = 7 + 5 + 5 = 17.



Q 15 :

Let A = {0, 1, 2, 3, 4, 5}. Let R be a relation on A defined by (x, y R if and only if max {x, y {3, 4}. Then among the statements

(S1) : The number of elements in R is 18, and

(S2) : The relation R is symmetric but neither reflexive nor transitive.           [2025]

  • both are true

     

  • only (S2) is true

     

  • both are false

     

  • only (S1) is true

     

(2)

R = {(0, 3), (3, 0), (0, 4), (4, 0), (1, 3), (3, 1), (2, 3), (3, 2), (3, 3), (1, 4), (4, 1), (2, 4), (4, 2), (3, 4), (4, 3), (4, 4)}

   Number of elements in R = 16

   S1 is false.

Now, (0, 0), (1, 1), (2, 2), (5, 5)  R    R is not reflexive.

Again, let (a, b R then (b, a R

As max {a, b} = max {b, a}    R is symmetric.

Now, R is not transitive as (0, 3), (3, 1)  R but (0, 1)  R.

   S2 is true.



Q 16 :

The number of non-empty equivalence relations on the set {1, 2, 3} is:          [2025]

  • 5

     

  • 6

     

  • 7

     

  • 4

     

(1)

Partitions of set {1, 2, 3} is {{1}}, {2}, {3}}, {{1, 2}, {3}}, {{1, 3}, {2}}, {{2, 3}, {1}}, {{1, 2, 3}}

   Number of non-empty equivalence relations on the set {1, 2, 3} = 5.



Q 17 :

Let R = {(1, 2), (2, 3), (3, 3)} be a relation defined on the set {1, 2, 3, 4}. Then the minimum number of elements, needed to be added in R so that R becomes an equivalence relation, is:          [2025]

  • 7

     

  • 10

     

  • 9

     

  • 8

     

(1)

Let A = {1, 2, 3, 4}

R = {(1, 2), (2, 3), (3, 3)}          [Given]

For an equivalence relation 'R' should be reflexive, symmetric and transitive.

   Minimum elements that should be added are

(2, 1), (3, 2), (1, 1), (2, 2), (4, 4), (1, 3), (3, 1)

   Minimum number of elements required = 7.



Q 18 :

Let A={(x,y)R×R:|x+y|3} and B={(x,y)R×R:|x|+|y|3}

If C={(x,y)AB:x=0 or y=0}, then (x,y)C|x+y| is:          [2025]

  • 18

     

  • 12

     

  • 24

     

  • 15

     

(2)

We have, A={(x,y)R×R:|x+y|3} and B={(x,y)R×R:|x|+|y|3}

From given figure, we get C = {(3, 0), (–3, 0), (0, 3), (0, –3)}

(x,y)C|x+y|=12



Q 19 :

Let X = R × R. Define a relation R on X as:

(a1,b1)R(a2,b2)b1=b2.

Statement I: R is an equivalence relation.

Statement II: For some (a, b X, the set

S = {(x, y X :(x, y) R (a, b)} represents a line parallel to y = x.

In the light of the above statements, choose the correct answer from the options given below:          [2025]

  • Statement I is true but Statement II is false.

     

  • Statement I is false but State II is true.

     

  • Both Statement I and Statement II are false.

     

  • Both Statement I and Statement II is true.

     

(1)

Statement I:

Reflexive : (a1,b1)R(a1,b1)b1=b1

   R is reflexive.

Symmetric : (a1,b1)R(a2,b2)b1=b2

                    (a2,b2)R(a1,b1)b2=b1

   R is symmetric.

Transitive : (a1,b1)R(a2,b2)b1=b2

and (a2,b2)R(a3,b3)b2=b3b1=b3

(a1,b1)R(a3,b3)

Hence, relation R is equivalence relation.

  Statement I is true.

For Statement II: (x, y) R (a, b), for some (a,b)Xy=b

So, Statement II is false.



Q 20 :

The relation R = {(x, y) : x, y  Z and x + y is even} is:          [2025]

  • reflexive and transitive but not symmetric.

     

  • reflexive and symmetric but not transitive.

     

  • symmetric and transitive but not reflexive.

     

  • an equivalence relation.

     

(4)

R = {(x, y) : x, y  Z and x + y is even}

For reflexive : x + x = 2x is even

For symmetric : x + y = y + x is even

For transitive : x + y is even and y + z is even then z + x is also even.

So, the relation is an equivalence.



Q 21 :

Define a relation R on the interval [0,π2) by xRy if and only if sec2xtan2y=1. Then R is :          [2025]

  • an equivalence relation.

     

  • reflexive but neither symmetric not transitive.

     

  • both reflexive and symmetric but not transitive.

     

  • both reflexive and transitive but not symmetric.

     

(1)

sec2xtan2x=1, x[0,π2)

   R is reflexive

Consider, sec2xtan2y=1

 1+tan2x(sec2y1)=1

 1+tan2xsec2y+1=1  sec2ytan2x=1

   R is symmetric.

Now, if sec2xtan2y=1 and sec2ytan2z=1

Adding both equation, sec2xtan2y+sec2ytan2z=2

 sec2xtan2z=1        [ sec2ytan2y=1]

   R is transitive

Thus R is an equivalence relation.



Q 22 :

Let S=N{0}. Define a relation R from S to R by:

R={(x,y):logey=xloge(25), xS, yR}

Then, the sum of all the elements in the range of R is equal to:          [2025]

  • 52

     

  • 53

     

  • 32

     

  • 109

     

(2)

We have, S=N{0}={0,1,2,3,......}

Also, logey=xloge(25)y=(25)x

   Required sum = (25)0+(25)1+(25)2+........

                              =1125=53.



Q 23 :

The number of relation on the set A = {1, 2, 3}, containing at most 6 elements including (1, 2), which are reflexive and transitive but not symmetric, is __________.          [2025]



(5)

Given, A = {1, 2, 3}

Let the relation be R on A, which is reflexive and transitive but not symmetric, then

(1, 1), (2, 2), (3, 3), (1, 2)  R

Remaining elements are

(2, 1), (2, 3), (1, 3), (3, 1), (3, 2)

Case I : If relation contains exactly 4 elements  1 way

Case II : If relation contains exactly 5 elements, so we can add (1, 3) or (3, 2)  2 ways

Case III : If relation contains exactly 6 elements, so we can add (2, 3), (1, 3) or (1, 3), (3, 2) or (3, 1), (3, 2)  3 ways

   Total number of relations is 6.



Q 24 :

Let A = {1, 2, 3}. The number of relations on A, containing (1, 2) and (2, 3), which are reflexive and transitive but not symmetric, is __________.          [2025]



(3)

For transitive : (1, 2) and (2, 3)  R  (1, 3)  R

For reflexive : (1, 1), (2, 2), (3, 3)  R

Now, for (2, 1), (3, 2), (3, 1); (3, 1) cannot be taken for not symmetric relation.

Case I : (2, 1) taken and (3, 2) not taken

Case II : (3, 2) taken and (2, 1) not taken

Case III : (2, 1) and (3, 2) are not taken

Therefore, 3 relations are possible.



Q 25 :

Let A={-2,-1,0,1,2,3,4}. Let R be a relation on A defined by xRy if and only if 2x+y2. Let l be the number of elements in R. Let m and n be the minimum number of elements required to be added in R to make it reflexive and symmetric relations respectively. Then l+m+n is equal to:                 [2026]

  • 33

     

  • 32

     

  • 35

     

  • 34

     

(1)

R = {(-2, a), (-1, b), (0, c), (1, d), (2, e)}

a = {-2, -1, 0, 1, 2, 3, 4};  
b = {-2, -1, 0, 1, 2, 3, 4}  
c = {-2, -1, 0, 1, 2};  
d = {-2, -1, 0};  
e = {-2}

∴ No. of elements in R  
= 7 + 7 + 5 + 3 + 1 = 23 =

Minimum number of element to be added to make it reflexive = m = 4  
⇒ {(1, 1), (2, 2), (3, 3), (4, 4)}

Minimum number of element to be added to make it symmetric = n = 6  

⇒ R = {(3, -2), (4, -2), (2, -1), (2, 0), (3, -1), (4, -1)}

+ m + n = 23 + 4 + 6 = 33



Q 26 :

Let R be a relation defined on the set {1,2,3,4}×{1,2,3,4} by R={((a,b),(c,d)):2a+3b=3c+4d}.

Then the number of elements in R  is                       [2026]

  • 15

     

  • 6

     

  • 18

     

  • 12

     

(4)

(a, b)      (c, d)

(1, 1)         x
(1, 2)         x
(1, 3)      (1, 2)
(1, 4)      (2, 2)
(2, 1)      (1, 1)
(2, 2)      (2, 1)
(2, 3)      (3, 1)
(2, 4)      (4, 1)
(3, 1)         x
(3, 2)         x
(3, 3)      (1, 3)
(3, 4)      (2, 3)
(4, 1)      (1, 2)
(4, 2)      (2, 2)
(4, 3)      (3, 2)
(4, 4)      (4, 2)



Q 27 :

Let the relation R on the set M={1,2,3,,16} be given by R={(x,y):4y=5x-3, x,yM}.

Then the minimum number of elements required to be added in R, in order to make the relation symmetric, is equal to         [2026]

  • 1

     

  • 2

     

  • 4

     

  • 3

     

(2)

R = {(3, 3), (7, 8), (11, 13)}

to make it symmetric (8, 7), (13, 11) must be added.



Q 28 :

Let A={0,1,2,,9} Let R be a relation on A defined by (x,y)R if and only if xy is a multiple of 3.

Given below are two statements:

Statement I: n(R)=36.

Statement II: R is an equivalence relation.

In the light of the above statements, choose the correct answer from the options given below. [2026]

  • Statement I is correct but Statement II is incorrect

     

  • Statement I is incorrect but Statement II is correct

     

  • Both Statement I and Statement II are incorrect

     

  • Both Statement I and Statement II are correct

     

(2)

Number of form 3K=4

Number of form 3K+1=3

Number of form 3K+2=4

4×4+3×3+3×3=34 relations

xRyyRx

(x-y)=3λ, (y-z)=3μ

(x-z)=3(λ+μ)

R is reflexive, symmetric and transitive S2 is true

Ans. S1 is false but S2 is true



Q 29 :

Let A = {2,3,5,7,9} Let R be the relation on A defined by xRy if and only if 2x3y. Let l be the number of elements in R, and m be the minimum number of elements required to be added in R to make it a symmetric relation. Then l+m is equal to :         [2026]

  • 25

     

  • 23

     

  • 27

     

  • 21

     

(1)

A={2,3,5,7,9}

y2x3

x=2,y=2,3,5,7,9x=3,y=2,3,5,7,9x=5,y=5,7,9x=7,y=5,7,9x=9,y=7,9]=18

To make it symmetric the elements to be added are {(5,2),(7,2),(9,2),(5,3),(7,3),(9,3),(9,5)}

m=7

 +m=25



Q 30 :

The number of elements in the relation R={(x,y):4x2+y2<52, x,y} is    [2026]

  • 86

     

  • 89

     

  • 67

     

  • 77

     

(4)

4x2+y2<52       ,    x,y

     

0    0,±1,±2,±3,±4,±5,±6,±7    1×15=15

±1           0,±1,±2,±3,.....,±6    2×13=26

±2             0,±1,±2,±3,.....,±5     2×11=22      

±3                                 0,±1,±2,±3     2×7=14

Number of elements =15+26+22+14=77