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Standalone Questions
#1017
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 6th April Morning Shift
KNOWLEDGE
4 Marks
Let $A = {n \in [100, 700] \cap N : n$ is neither a multiple of 3 nor a multiple of 4}. Then the number of elements in $A$ is
(A) 300
(B) 310
(C) 290
(D) 280
Key: A
Sol:
Sol:
Let's find the total number of integers in the range $[100, 700]$. The total number of integers is $700 - 100 + 1 = 601$. Thus, the total number of integers is $601$.
Let $n(3)$ be the number of multiples of 3 in the given range. The first multiple of 3 is $102 = 3 \times 34$ and the last multiple of 3 is $699 = 3 \times 233$. So, $n(3) = 233 - 34 + 1 = 200$.
Let $n(4)$ be the number of multiples of 4 in the given range. The first multiple of 4 is $100 = 4 \times 25$ and the last multiple of 4 is $700 = 4 \times 175$. So, $n(4) = 175 - 25 + 1 = 151$.
Let $n(12)$ be the number of multiples of 12 in the given range. The first multiple of 12 is $108 = 12 \times 9$ and the last multiple of 12 is $696 = 12 \times 58$. So, $n(12) = 58 - 9 + 1 = 50$.
The number of elements in A is given by the total number of elements minus (multiples of 3 + multiples of 4) + (multiples of 12)
$n(A) = 601 - (200 + 151) + 50 = 601 - 351 + 50 = 250 + 50 = 300$.
Therefore, the number of elements in A is $300$.
#1015
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2024
JEE Main 2024 (Online) 8th April Evening Shift
KNOWLEDGE
4 Marks
Let $A = {2, 3, 6, 8, 9, 11}$ and $B = {1, 4, 5, 10, 15}$. Let $R$ be a relation on $A \times B$ defined by $(a, b)R(c, d)$ if and only if $3ad - 7bc$ is an even integer. Then the relation $R$ is
(A) reflexive but not symmetric.
(B) an equivalence relation.
(C) reflexive and symmetric but not transitive.
(D) transitive but not symmetric.
Key: C
Sol:
Sol:
Given that $(a, b)R(c, d) \Rightarrow 3ad - 7bc \in \text{even}$.
For reflexive, we need to check if $(a, b)R(a, b)$.
$(a, b)R(a, b) \Rightarrow 3ab - 7ba = -4ab \in \text{even}$. This is true since the product $ab$ will be an integer, and $-4$ times an integer is even.
Thus, $R$ is reflexive.
For symmetric, if $(a, b)R(c, d)$, then $(c, d)R(a, b)$ must also be true.
$(a, b)R(c, d) \Rightarrow 3ad - 7bc = 2m$ for some integer $m$.
$(c, d)R(a, b) \Rightarrow 3cb - 7ad$. We want to show this is even.
$3cb - 7ad = -7ad + 3cb = -(7ad - 3cb) = -(7ad - 3cb + 3ad - 3ad - 7bc + 7bc) = -(10ad - 10bc - (3ad - 7bc)) = -10(ad - bc) + (3ad-7bc)$
#1014
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 22nd January Morning Shift
KNOWLEDGE
4 Marks
The number of non-empty equivalence relations on the set ${1, 2, 3}$ is :
(A) $7$
(B) $4$
(C) $5$
(D) $6$
Key: C
Sol:
Sol:
An equivalence relation on a finite set is uniquely determined by its partition into equivalence classes. Counting the number of ways to partition the set ${1, 2, 3}$:
1. Three blocks: Each element in its own block. There is only one way: ${{1}, {2}, {3}}$.
2. Two blocks: We can have ${{1, 2}, {3}}$, ${{1, 3}, {2}}$, or ${{2, 3}, {1}}$. There are 3 ways.
3. One block: All elements together. There is only one way: ${{1, 2, 3}}$.
In total, there are $1 + 3 + 1 = 5$ distinct partitions, which means there are 5 equivalence relations on the set ${1, 2, 3}$.
#1013
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 22nd January Morning Shift
KNOWLEDGE
4 Marks
Let $A = {1, 2, 3, …, 10}$ and $B = {\frac{m}{n} : m, n \in A, m < n$ and $gcd(m, n) = 1}$. Then $n(B)$ is equal to :
(A) $29$
(B) $31$
(C) $37$
(D) $36$
Key: B
Sol:
Sol:
To find the number of elements in set $B$, we consider pairs $(\frac{m}{n})$ where $m, n \in A$ with $m < n$ and $gcd(m, n) = 1$.
Here's the breakdown for each possible $m$:
For $m = 1$:
Possible values for $n$ are $2, 3, 4, 5, 6, 7, 8, 9, 10$.
Total pairs: $9$.
For $m = 2$:
Possible values for $n$ are $3, 5, 7, 9$ (since these have $gcd(2, n) = 1$).
Total pairs: $4$.
For $m = 3$:
Possible values for $n$ are $4, 5, 7, 8, 10$.
Total pairs: $5$.
For $m = 4$:
Possible values for $n$ are $5, 7, 9$.
Total pairs: $3$.
For $m = 5$:
Possible values for $n$ are $6, 7, 8, 9$.
Total pairs: $4$.
For $m = 6$:
Possible value for $n$ is $7$.
Total pairs: $1$.
For $m = 7$:
Possible values for $n$ are $8, 9, 10$.
Total pairs: $3$.
For $m = 8$:
Possible value for $n$ is $9$.
Total pairs: $1$.
For $m = 9$:
Possible value for $n$ is $10$.
Total pairs: $1$.
Adding all these up, the total number of elements in set $B$ is:
$9 + 4 + 5 + 3 + 4 + 1 + 3 + 1 + 1 = 31$
#1012
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 23rd January Morning Shift
KNOWLEDGE
4 Marks
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:
(A) 9
(B) 8
(C) 7
(D) 10
Key: C
Sol:
Sol:
For $R$ to be an equivalence relation on $A = \{1, 2, 3, 4\}$, it must be reflexive, symmetric and transitive.
1. **Reflexive:** $R$ must contain $(1, 1), (2, 2), (3, 3), (4, 4)$. Since $(3,3)$ is already in $R$, we need to add $(1, 1), (2, 2), (4, 4)$.
2. **Symmetric:** $R$ must contain $(2, 1)$ and $(3, 2)$ because it contains $(1, 2)$ and $(2, 3)$.
3. **Transitive:** Since $(1, 2)$ and $(2, 3)$ are in $R$, $(1, 3)$ must also be in $R$. And since we added $(3,2)$ now we must add $(1,2)$. Which already exists.
So, the minimum elements to be added are:
$(1, 1), (2, 2), (4, 4), (2, 1), (3, 2), (1, 3)$.
Therefore, the minimum number of elements to be added is $7$.
#1011
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 23rd January Evening Shift
KNOWLEDGE
4 Marks
Let $A = {(x, y) ∈ R × R : |x + y| ⩾ 3}$ and $B = {(x, y) ∈ R × R : |x| + |y| ≤ 3}$. If $C = {(x, y) ∈ A ∩ B : x = 0$ or $y = 0}$, then $\sum_{(x, y) ∈ C} |x + y|$ is :
(A) 18
(B) 24
(C) 15
(D) 12
Key: D
Sol:
Sol:
From the image, we can determine that the points in set C are $(3,0)$, $(-3,0)$, $(0,3)$ and $(0,-3)$.
Thus, $C = {(3, 0), (-3, 0), (0, 3), (0, -3)}$.
$\sum |x + y| = |3 + 0| + |-3 + 0| + |0 + 3| + |0 + (-3)| = 3 + 3 + 3 + 3 = 12$.
#1010
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 23rd January Evening Shift
KNOWLEDGE
4 Marks
Let $X = R \times R$. Define a relation R on X as: $(a_1, b_1) R (a_2, b_2) \Leftrightarrow b_1 = b_2$ Statement I: $R$ is an equivalence relation. Statement II: For some $(a, b) \in X$, the set $S = \{(x, y) \in X : (x, y)R(a, b)\}$ represents a line parallel to $y = x$. In the light of the above statements, choose the correct answer from the options given below:
(A) Both Statement I and Statement II are true
(B) Statement I is true but Statement II is false
(C) Both Statement I and Statement II are false
(D) Statement I is false but Statement II is true
Key: B
Sol:
Sol:
Statement I: Reflexive: $(a_1, b_1) R (a_1, b_1) \Rightarrow b_1 = b_1$ (True). Symmetric: $(a_1, b_1) R (a_2, b_2) \Rightarrow b_1 = b_2$ and $(a_2, b_2) R (a_1, b_1) \Rightarrow b_2 = b_1$ (True). Transitive: $(a_1, b_1) R (a_2, b_2) \Rightarrow b_1 = b_2$ and $(a_2, b_2) R (a_3, b_3) \Rightarrow b_2 = b_3$. Thus, $b_1 = b_3$, so $(a_1, b_1) R (a_3, b_3)$ (True). Hence, relation $R$ is an equivalence relation, and Statement I is true. For Statement II: $(x, y) R (a, b) \Rightarrow y = b$. This represents a line $y=b$, which is parallel to the x-axis. It is not parallel to the line $y=x$. Therefore, Statement II is false.
#1009
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 24th January Evening Shift
KNOWLEDGE
4 Marks
Let $A = {x \in (0, \pi) - {\frac{\pi}{2}} : \log_{(2/\pi)} |\sin x| + \log_{(2/\pi)} |\cos x| = 2}$ and $B = {x \ge 0 : x(x-4) - 3|x-2| + 6 = 0}$. Then $n(A \cup B)$ is equal to :
(A) 4
(B) 8
(C) 6
(D) 2
Key: B
Sol:
Sol:
For set A: $\log_{\frac{2}{\pi}} |\sin x| + \log_{\frac{2}{\pi}} |\cos x| = 2$ $\Rightarrow \log_{\frac{2}{\pi}} |\sin x \cdot \cos x| = 2$ $\Rightarrow |\sin x \cos x| = (\frac{2}{\pi})^2$ $\Rightarrow |\frac{1}{2} \sin 2x| = \frac{4}{\pi^2}$ $\Rightarrow |\sin 2x| = \frac{8}{\pi^2}$ Since $0 < \frac{8}{\pi^2} < 1$, there are 4 solutions for $x \in (0, \pi)$. For set B: Case 1: $x < 2$, $x(x-4) + 3(x-2) + 6 = 0$ $\Rightarrow x^2 - 4x + 3x - 6 + 6 = 0$ $\Rightarrow x^2 - x = 0$ $\Rightarrow x(x-1) = 0$, so $x = 0, 1$. Case 2: $x > 2$, $x(x-4) - 3(x-2) + 6 = 0$ $\Rightarrow x^2 - 4x - 3x + 6 + 6 = 0$ $\Rightarrow x^2 - 7x + 12 = 0$ $\Rightarrow (x-3)(x-4) = 0$, so $x = 3, 4$. Thus, $B = {0, 1, 3, 4}$, so $n(B) = 4$. Since $A$ and $B$ are disjoint, $n(A \cup B) = n(A) + n(B) = 4 + 4 = 8$.
#1008
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 28th January Morning Shift
KNOWLEDGE
4 Marks
The relation $R = {(x, y) : x, y ∈ Z$ and $x + y$ is even $}$ is:
(A) reflexive and transitive but not symmetric
(B) reflexive and symmetric but not transitive
(C) an equivalence relation
(D) symmetric and transitive but not reflexive
Key: C
Sol:
Sol:
The given relation is $R = {(x, y) : x, y ∈ Z$ and $x + y$ is even $}$.
Reflexive: For any $x ∈ Z$, $x + x = 2x$, which is even. So, $(x, x) ∈ R$. Thus, $R$ is reflexive.
Symmetric: If $(x, y) ∈ R$, then $x + y$ is even. Since $x + y = y + x$, $y + x$ is also even. So, $(y, x) ∈ R$. Thus, $R$ is symmetric.
Transitive: If $(x, y) ∈ R$ and $(y, z) ∈ R$, then $x + y$ is even and $y + z$ is even. Then $(x + y) + (y + z) = x + 2y + z$ is even. Since $2y$ is even, it follows that $x + z$ is even. So, $(x, z) ∈ R$. Thus, $R$ is transitive.
Since $R$ is reflexive, symmetric, and transitive, it is an equivalence relation.
#1007
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 29th January Morning Shift
KNOWLEDGE
4 Marks
Define a relation R on the interval $[0, π/2)$ by $x$ R $y$ if and only if $\sec^2x - \tan^2y = 1$. Then R is :
(A) both reflexive and symmetric but not transitive
(B) both reflexive and transitive but not symmetric
(C) reflexive but neither symmetric not transitive
(D) an equivalence relation
Key: D
Sol:
Sol:
To check if the relation R is reflexive, symmetric, and transitive:
1. **Reflexive:**
Replace $y$ with $x$ in the given relation: $\sec^2x - \tan^2x = 1$. This is a trigonometric identity, so the relation is reflexive.
2. **Symmetric:**
Given $\sec^2x - \tan^2y = 1$, we can rewrite this as $1 + \tan^2x - \tan^2y = 1$, which implies $\tan^2x = \tan^2y$. Also, $\sec^2x - \tan^2y = 1$ can be rewritten as $1 + \tan^2x - \sec^2y + 1 = 1$, leading to $\sec^2y - \tan^2x = 1$. Thus, if $xRy$, then $yRx$, so the relation is symmetric.
3. **Transitive:**
Suppose $\sec^2x - \tan^2y = 1$ and $\sec^2y - \tan^2z = 1$. Adding these two equations, we get:
$\sec^2x - \tan^2y + \sec^2y - \tan^2z = 1 + 1$
$\sec^2x + (\sec^2y - \tan^2y) - \tan^2z = 2$
Since $\sec^2y - \tan^2y = 1$, we have:
$\sec^2x + 1 - \tan^2z = 2$
$\sec^2x - \tan^2z = 1$
Thus, if $xRy$ and $yRz$, then $xRz$, so the relation is transitive.
Since the relation is reflexive, symmetric, and transitive, it is an equivalence relation.
#1006
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 29th January Evening Shift
KNOWLEDGE
4 Marks
Let $S = \mathbb{N} \cup \{0\}$. Define a relation R from S to $\mathbb{R}$ by: $R = \{(x, y) : \log_e y = x \log_e (\frac{2}{5}), x \in S, y \in \mathbb{R}\}$. Then, the sum of all the elements in the range of $R$ is equal to:
(A) $\frac{3}{2}$
(B) $\frac{10}{9}$
(C) $\frac{5}{2}$
(D) $\frac{5}{3}$
Key: D
Sol:
Sol:
Given $S = \{0, 1, 2, 3, ...\}$. Also, $\log_e y = x \log_e (\frac{2}{5})$.
This implies $y = (\frac{2}{5})^x$.
Since $x \in S$, $x$ can take values $0, 1, 2, 3, ...$.
The required sum is $1 + (\frac{2}{5})^1 + (\frac{2}{5})^2 + (\frac{2}{5})^3 + ... = \frac{1}{1 - \frac{2}{5}} = \frac{1}{\frac{3}{5}} = \frac{5}{3}$.
#1003
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 3rd April Morning Shift
KNOWLEDGE
4 Marks
Let $A = {-3, -2, -1, 0, 1, 2, 3}$. Let R be a relation on A defined by $xRy$ if and only if $0 \le x^2 + 2y \le 4$. 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 reflexive relation. Then $l + m$ is equal to
(A) 18
(B) 20
(C) 17
(D) 19
Key: A
Sol:
Sol:
First, we determine the pairs $(x, y)$ that satisfy the condition $0 \le x^2 + 2y \le 4$ for the given set $A = \{-3, -2, -1, 0, 1, 2, 3\}$.
For $y = -3$, $x^2 + 2(-3) \le 4 \implies x^2 \le 10$, so $x$ can be $-3$ or $3$.
For $y = -2$, $x^2 + 2(-2) \le 4 \implies x^2 \le 8$, so $x$ can be $-2$ or $2$.
For $y = -1$, $x^2 + 2(-1) \le 4 \implies x^2 \le 6$, so $x$ can be $-2$ or $2$.
For $y = 0$, $x^2 + 2(0) \le 4 \implies x^2 \le 4$, so $x$ can be $-2, -1, 0, 1, 2$.
For $y = 1$, $x^2 + 2(1) \le 4 \implies x^2 \le 2$, so $x$ can be $-1, 0, 1$.
For $y = 2$, $x^2 + 2(2) \le 4 \implies x^2 \le 0$, so $x$ can only be $0$.
Thus, the relation R consists of the following pairs:
$R = \{(3, -3), (-3, -3), (-2, -2), (2, -2), (-2, -1), (2, -1), (-2, 0), (-1, 0), (0, 0), (1, 0), (2, 0), (-1, 1), (0, 1), (1, 1), (0, 2)\}$.
The number of elements in R is $l = 15$.
To make R reflexive, it must include all pairs $(x, x)$ for every $x \in A$. The set A has 7 elements, so the reflexive relation must contain $(-3, -3), (-2, -2), (-1, -1), (0, 0), (1, 1), (2, 2), (3, 3)$. Currently, R has $(-3,-3), (-2, -2), (0,0), (1,1)$. So the missing pairs are $(-1, -1), (2, 2), (3, 3)$, meaning $m = 3$.
Therefore, $l + m = 15 + 3 = 18$.
#1001
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 4th April Morning Shift
KNOWLEDGE
4 Marks
Consider the sets $A = \{(x, y) \in R \times R : x^2 + y^2 = 25\}$, $B = \{(x, y) \in R \times R : x^2 + 9y^2 = 144\}$, $C = \{(x, y) \in Z \times Z : x^2 + y^2 \le 4\}$ and $D = A \cap B$. The total number of one-one functions from the set $D$ to the set $C$ is:
(A) $15120$
(B) $18290$
(C) $17160$
(D) $19320$
Key: C
Sol:
Sol:
The given sets are $A = \{(x, y) \in R \times R : x^2 + y^2 = 25\}$ and $B = \{(x, y) \in R \times R : x^2 + 9y^2 = 144\}$. To find the intersection of A and B, we solve the system of equations. Subtracting the equation for A from the equation for B gives: $x^2 + 9y^2 - (x^2 + y^2) = 144 - 25$, which simplifies to $8y^2 = 119$, so $y^2 = \frac{119}{8}$. Substituting this into the equation for A, we get $x^2 = 25 - \frac{119}{8} = \frac{200 - 119}{8} = \frac{81}{8}$. Thus, $x = \pm \frac{9}{\sqrt{8}}$ and $y = \pm \frac{\sqrt{119}}{\sqrt{8}}$. Since $D = A \cap B$, the set D contains 4 points. Now, consider the set $C = \{(x, y) \in Z \times Z : x^2 + y^2 \le 4\}$. The integer pairs (x, y) that satisfy this condition are: $(\pm 2, 0)$, $(0, \pm 2)$, $(\pm 1, 0)$, $(0, \pm 1)$, $(\pm 1, \pm 1)$, and $(0, 0)$. Counting these points, we find that there are 13 such pairs. The number of one-to-one functions from D to C is the number of ways to choose 4 elements from C and arrange them, which is $P(13, 4) = \frac{13!}{(13-4)!} = \frac{13!}{9!} = 13 \times 12 \times 11 \times 10 = 17160$.
#999
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 7th April Evening Shift
KNOWLEDGE
4 Marks
Let $A = \{ (\alpha, \beta) \in R \times R : |\alpha - 1| \leq 4 \text{ and } |\beta - 5| \leq 6 \}$ and $B = \{ (\alpha, \beta) \in R \times R : 16(\alpha - 2)^2 + 9(\beta - 6)^2 \leq 144 \}$. Then
(A) $A \subset B$
(B) $B \subset A$
(C) neither $A \subset B$ nor $B \subset A$
(D) $A \cup B = \{ (x, y) : -4 \leqslant x \leqslant 4, -1 \leqslant y \leqslant 11 \}$
Key: B
Sol:
Sol:
For set A, we have $|x - 1| \leq 4$ and $|y - 5| \leq 6$. This implies $-4 \leq x - 1 \leq 4$ and $-6 \leq y - 5 \leq 6$. Therefore, $-3 \leq x \leq 5$ and $-1 \leq y \leq 11$. For set B, we have $16(x - 2)^2 + 9(y - 6)^2 \leq 144$, which simplifies to $\frac{(x - 2)^2}{9} + \frac{(y - 6)^2}{16} \leq 1$. This represents an ellipse centered at $(2, 6)$ with semi-major axis 4 and semi-minor axis 3. From the diagram, it's clear that $B \subset A$.
#998
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 8th April Evening Shift
KNOWLEDGE
4 Marks
Let $A = {0, 1, 2, 3, 4, 5}$. Let $R$ be a relation on $A$ defined by $(x, y) \in R$ if and only if $\max{x, y} \in {3, 4}$. 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
(S1): The number of elements in $R$ is $18$, and
(S2): The relation $R$ is symmetric but neither reflexive nor transitive
(A) both are false
(B) only (S1) is true
(C) only (S2) is true
(D) both are true
Key: C
Sol:
Sol:
To determine the elements in the relation $R$, we need to find all pairs $(x, y)$ such that $\max(x, y) \in {3, 4}$. The set $A = {0, 1, 2, 3, 4, 5}$.
If $\max(x, y) = 3$, the pairs are $(0, 3), (1, 3), (2, 3), (3, 3), (3, 0), (3, 1), (3, 2)$.
If $\max(x, y) = 4$, the pairs are $(0, 4), (1, 4), (2, 4), (3, 4), (4, 4), (4, 0), (4, 1), (4, 2), (4, 3)$.
Thus, the total number of elements in $R$ is $7 + 9 = 16$. Therefore, statement S1 is false.
For statement S2, we check the properties of $R$:
Reflexivity: $(0, 0)$ is not in $R$, so $R$ is not reflexive.
Symmetry: If $(x, y) \in R$, then $\max(x, y) \in {3, 4}$, which implies $\max(y, x) \in {3, 4}$, so $(y, x) \in R$. Thus, $R$ is symmetric.
Transitivity: $(0, 3) \in R$ and $(3, 1) \in R$, but $(0, 1)$ is not in $R$. Therefore, $R$ is not transitive.
Statement S2 is true since $R$ is symmetric but neither reflexive nor transitive.
#996
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 4th April Evening Shift
KNOWLEDGE
4 Marks
Let $A = \{-3, -2, -1, 0, 1, 2, 3\}$ and R be a relation on A defined by $xRy$ if and only if $2x - y \in \{0, 1\}$. 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:
(A) 17
(B) 18
(C) 15
(D) 16
Key: A
Sol:
Sol:
$xRy \Leftrightarrow 2x - y \in \{0, 1\}$
$\Rightarrow y = 2x$ or $y = 2x - 1$
$A=\{-3,-2,-1, 0, 1, 2, 3\}$
$R = \{(-1,-2), (0,0), (1, 2), (-1, -3), (0, -1), (1, 1), (2,3)\}$
$\Rightarrow I=7$
For $R$ to be reflexive $(0,0), (1,1) \in R$
But other $(a, a)$ such that $2a - a \in \{0, 1\}$
$\Rightarrow a \in \{0, 1\}$
5 other pairs needs to be added
$\Rightarrow m=5$
$xRy \Rightarrow yRx$ to be symmetric
$(-1, -2) \Rightarrow (-2, -1)$
$(1, 2) \Rightarrow (2, 1)$
$(-1, -3) \Rightarrow (-3, -1)$
$(0, -1) \Rightarrow (-1, 0)$
$(2, 3) \Rightarrow (3, 2)$
$\Rightarrow 5$ needs to be added, $n=5$
$\Rightarrow l+m+n=17$
#995
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2025
JEE Main 2025 (Online) 7th April Evening Shift
KNOWLEDGE
4 Marks
Let $A = { (\alpha, \beta ) \in R \times R : |\alpha - 1| \leq 4$ and $|\beta - 5| \leq 6 }$
and $B = { (\alpha, \beta ) \in R \times R : 16(\alpha - 2)^{2}+ 9(\beta - 6)^{2} \leq 144 }$.
Then
and $B = { (\alpha, \beta ) \in R \times R : 16(\alpha - 2)^{2}+ 9(\beta - 6)^{2} \leq 144 }$.
Then
(A) A $A \subset B$
(B) B $B \subset A$
(C) C neither $A \subset B$ nor $B \subset A$
(D) D $A \cup B = { (x, y) : -4 \leqslant x \leqslant 4, -1 \leqslant y \leqslant 11 }$
Key: B
Sol:
Sol:
$A: |x-1| \leq 4$ and $|y-5| \leq 6$
$\Rightarrow -4 \leq x-1 \leq 4 \Rightarrow -6 \leq y-5 \leq 6$
$\Rightarrow -3 \leq x \leq 5 \Rightarrow -1 \leq y \leq 11$
$B : 16(x-2)^{2} + 9(y-6)^{2} \leq 144$
$B : \frac{(x-2)^{2}}{9} + \frac{(y-6)^{2}}{16} \leq 1$
From Diagram $B \subset A$
#993
Mathematics
Statistics and Probability
MCQ_SINGLE
APPLY
EASY
2025
JEE Main 2025 (Online) 28th January Morning Shift
KNOWLEDGE
4 Marks
Three defective oranges are accidently mixed with seven good ones and on looking at them, it is not possible to differentiate between them. Two oranges are drawn at random from the lot. If $x$ denote the number of defective oranges, then the variance of $x$ is
(A) 26/75
(B) 14/25
(C) 18/25
(D) 28/75
Key: D
Sol:
Sol:
Probability distribution
$x = 0$, $p = \frac{^7C_2}{^{10}C_2} = \frac{42}{90}$
$x = 1$, $p = \frac{^7C_1 \times ^3C_1}{^{10}C_2} = \frac{42}{90}$
$x = 2$, $p = \frac{^3C_2}{^{10}C_2} = \frac{6}{90}$
Now,
$\mu = \sum x_i p_i = \frac{42}{90} + \frac{12}{90} = \frac{54}{90}$
$\sigma^2 = \sum p_i x_i^2 - \mu^2 = \frac{42}{90} + \frac{24}{90} - (\frac{54}{90})^2$
$\Rightarrow \frac{66}{90} - (\frac{54}{90})^2$
$\sigma^2 \Rightarrow \frac{28}{75}$
#992
Mathematics
Statistics and Probability
MCQ_SINGLE
APPLY
EASY
2025
JEE Main 2025 (Online) 28th January Morning Shift
KNOWLEDGE
4 Marks
Two number $k_1$ and $k_2$ are randomly chosen from the set of natural numbers. Then, the probability that the value of $i^{k_1} + i^{k_2}$, ($i = \sqrt{-1}$) is non-zero, equals
(A) $\frac{3}{4}$
(B) $\frac{1}{2}$
(C) $\frac{1}{4}$
(D) $\frac{2}{3}$
Key: A
Sol:
Sol:
$i^{k_1} + i^{k_2} \ne 0 \Rightarrow i^{k_1} \rightarrow 4$ option for $i, -1, -i, 1$
Total cases $ \Rightarrow 4 \times 4 = 16$
Unfovourble cases $ \Rightarrow i^{k_1} + i^{k_2} = 0$
$ \{\begin{array}{c}1, -1 \\ -1, 1 \\ i, -i \\ -i, i\end{array}\}$
4 Cases $\Rightarrow$ Probability $ = \frac{16-4}{16} = \frac{3}{4}$
#991
Mathematics
Statistics and Probability
MCQ_SINGLE
APPLY
EASY
2025
JEE Main 2025 (Online) 28th January Evening Shift
KNOWLEDGE
4 Marks
Let S be the set of all the words that can be formed by arranging all the letters of the word GARDEN. From the set S, one word is selected at random. The probability that the selected word will NOT have vowels in alphabetical order is:
(A) $\frac{1}{4}$
(B) $\frac{1}{2}$
(C) $\frac{1}{3}$
(D) $\frac{2}{3}$
Key: B
Sol:
Sol:
A, E,G R D N
Probabllity $(P) = \frac{\text{favourable case}}{\text{Total case}}$
(when A & E are in order)
Total case = $6!$
Favourable case = ${6}C_2 . 4! = (15)4! = (30)4!$
$P = \frac{(15)4!}{(30)4!} = \frac{1}{2}$
Probability when not in order = $1 - \frac{1}{2} = \frac{1}{2}$