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Standalone Questions
#1066
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2018
JEE Main 2018 (Offline)
KNOWLEDGE
4 Marks
Two sets A and B are as under : A = {$(a, b) ∈ R × R : |a - 5| < 1$ and $|b - 5| < 1$}; B = {$(a, b) ∈ R × R : 4(a - 6)^2 + 9(b - 5)^2 ≤ 36$}; Then
(A) neither A ⊂ B nor B ⊂ A
(B) B ⊂ A
(C) A ⊂ B
(D) A ∩ B = 𝜙 ( an empty set )
Key: C
Sol:
Sol:
Given, $4(a-6)^2 + 9(b-5)^2 ≤ 36$. Let $a-6 = x$ and $b-5 = y$. Therefore, $4x^2 + 9y^2 ≤ 36$, which implies $\frac{x^2}{9} + \frac{y^2}{4} ≤ 1$. This is the equation of an ellipse.
According to set A, $|a-5| < 1$, which implies, since $a-6=x$, then $a-5 = x+1$. Thus $|x+1| < 1$, implying $-1 < x+1 < 1$, which leads to $-2 < x < 0$. Similarly, $|b-5| < 1$, implying $|y| < 1$, which leads to $-1 < y < 1$.
To check if the entire set A is inside of B, we can test a point of set A in the inequality $\frac{x^2}{9} + \frac{y^2}{4} ≤ 1$. Consider the point $(-2, 1)$. Substituting into the inequality gives LHS = $\frac{(-2)^2}{9} + \frac{1^2}{4} = \frac{4}{9} + \frac{1}{4} = \frac{25}{36} < 1$. Since the inequality holds, $(-2, 1)$ is inside the ellipse. Similarly, $(-2, -1)$ is also inside the ellipse. Hence, we can say that entire set A is inside of set B, therefore $A ⊂ B$.
#1065
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2018
JEE Main 2018 (Online) 16th April Morning Slot
KNOWLEDGE
4 Marks
Let $N$ denote the set of all natural numbers. Define two binary relations on $N$ as $R_1 = \{(x, y) \in N \times N : 2x + y = 10\}$ and $R_2 = \{(x, y) \in N \times N : x + 2y = 10\}$. Then :
(A) Range of $R_1$ is $\{2, 4, 8\}$.
(B) Range of $R_2$ is $\{1, 2, 3, 4\}$.
(C) Both $R_1$ and $R_2$ are symmetric relations.
(D) Both $R_1$ and $R_2$ are transitive relations.
Key: B
Sol:
Sol:
For $R_1$, $2x + y = 10$ and $x, y \in N$, the possible values for $x$ and $y$ are:
$x = 1, y = 8 \implies (1, 8)$
$x = 2, y = 6 \implies (2, 6)$
$x = 3, y = 4 \implies (3, 4)$
$x = 4, y = 2 \implies (4, 2)$
Therefore, $R_1 = \{(1, 8), (2, 6), (3, 4), (4, 2)\}$.
Hence, the range of $R_1$ is $\{2, 4, 6, 8\}$.
$R_1$ is not symmetric.
$R_1$ is not transitive as $(3, 4), (4, 2) \in R_1$, but $(3, 2) \notin R_1$.
For $R_2$, $x + 2y = 10$ and $x, y \in N$, the possible values for $x$ and $y$ are:
$x = 8, y = 1 \implies (8, 1)$
$x = 6, y = 2 \implies (6, 2)$
$x = 4, y = 3 \implies (4, 3)$
$x = 2, y = 4 \implies (2, 4)$
Therefore, $R_2 = \{(8, 1), (6, 2), (4, 3), (2, 4)\}$.
Hence, the range of $R_2 = \{1, 2, 3, 4\}$.
$R_2$ is not symmetric and transitive.
#1064
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2019
JEE Main 2019 (Online) 10th January Morning Slot
KNOWLEDGE
4 Marks
In a class of $140$ students numbered $1$ to $140$, all even numbered students opted Mathematics course, those whose number is divisible by $3$ opted Physics course and those whose number is divisible by $5$ opted Chemistry course. Then the number of students who did not opt for any of the three courses is
(A) $42$
(B) $102$
(C) $1$
(D) $38$
Key: D
Sol:
Sol:
Let $A$ be the set of students who opted for Mathematics, $B$ be the set of students who opted for Physics, and $C$ be the set of students who opted for Chemistry. We are given:
Total number of students $= 140$
$n(A) = \lfloor\frac{140}{2}\rfloor = 70$
$n(B) = \lfloor\frac{140}{3}\rfloor = 46$
$n(C) = \lfloor\frac{140}{5}\rfloor = 28$
$n(A \cap B) = \lfloor\frac{140}{6}\rfloor = 23$
$n(B \cap C) = \lfloor\frac{140}{15}\rfloor = 9$
$n(C \cap A) = \lfloor\frac{140}{10}\rfloor = 14$
$n(A \cap B \cap C) = \lfloor\frac{140}{30}\rfloor = 4$
Using the principle of inclusion-exclusion:
$n(A \cup B \cup C) = n(A) + n(B) + n(C) - n(A \cap B) - n(B \cap C) - n(C \cap A) + n(A \cap B \cap C)$
$n(A \cup B \cup C) = 70 + 46 + 28 - 23 - 9 - 14 + 4 = 102$
The number of students who did not opt for any of the three courses is:
$140 - n(A \cup B \cup C) = 140 - 102 = 38$
#1063
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2019
JEE Main 2019 (Online) 12th January Morning Slot
KNOWLEDGE
4 Marks
Let $S = {1, 2, 3, … , 100}$. The number of non-empty subsets A of S such that the product of elements in A is even is :
(A) $2^{50} – 1$
(B) $2^{50} (2^{50} – 1)$
(C) $2^{100} – 1$
(D) $2^{50} + 1$
Key: B
Sol:
Sol:
Let $S = {1, 2, 3, ..., 100}$. The total number of non-empty subsets is $2^{100} - 1$. The number of subsets with an odd product consists only of odd numbers. There are 50 odd numbers in the set $S$. So, the number of such subsets is $2^{50} - 1$. Therefore, the number of subsets with an even product is $(2^{100} - 1) - (2^{50} - 1) = 2^{100} - 2^{50} = 2^{50}(2^{50} - 1)$.
#1062
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2019
JEE Main 2019 (Online) 12th January Evening Slot
KNOWLEDGE
4 Marks
Let $Z$ be the set of integers. If $A = {x \in Z : 2(x + 2) (x^2 - 5x + 6) = 1}$ and $B = {x \in Z : -3 < 2x - 1 < 9}$, then the number of subsets of the set $A \times B$, is
(A) $2^{12}$
(B) $2^{18}$
(C) $2^{10}$
(D) $2^{15}$
Key: D
Sol:
Sol:
Given $A = {x \in Z : 2(x+2)(x^2 - 5x + 6) = 1}$.
Since $2(x+2)(x^2 - 5x + 6) = 1$, we can rewrite it as $2(x+2)(x^2 - 5x + 6) = 2^0$.
This implies that $x = -2, 2, 3$, so $A = {-2, 2, 3}$.
Also, $B = {x \in Z : -3 < 2x - 1 < 9}$.
Adding 1 to all sides, we get $-2 < 2x < 10$.
Dividing by 2, we get $-1 < x < 5$.
Thus, $B = {0, 1, 2, 3, 4}$.
Now, $A \times B$ has $3 \times 5 = 15$ elements.
The number of subsets of $A \times B$ is $2^{15}$.
#1061
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2019
JEE Main 2019 (Online) 9th April Evening Slot
KNOWLEDGE
4 Marks
Two newspapers A and B are published in a city. It is known that $25$% of the city populations reads A and $20$% reads B while $8$% reads both A and B. Further, $30$% of those who read A but not B look into advertisements and $40$% of those who read B but not A also look into advertisements, while $50$% of those who read both A and B look into advertisements. Then the percentage of the population who look into advertisement is :-
(A) $13.5$
(B) $13$
(C) $12.8$
(D) $13.9$
Key: D
Sol:
Sol:
Let the total population be $100$. Then:
People who read A only: $25 - 8 = 17$
People who read B only: $20 - 8 = 12$
People who read A and look into advertisements: $0.30 \times 17 = 5.1$
People who read B and look into advertisements: $0.40 \times 12 = 4.8$
People who read both A and B and look into advertisements: $0.50 \times 8 = 4$
Total percentage of people who look into advertisements: $5.1 + 4.8 + 4 = 13.9$
Therefore, the percentage of the population who look into advertisement is $13.9$%.
#1060
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2019
JEE Main 2019 (Online) 12th April Evening Slot
KNOWLEDGE
4 Marks
Let A, B and C be sets such that $\phi \neq A \cap B \subseteq C$. Then which of the following statements is not true ?
(A) If (A – B) $\subseteq$ C, then A $\subseteq$ C
(B) B $\cap$ C $\neq$ $\phi$
(C) (C $\cup$ A) $\cap$ (C $\cup$ B) = C
(D) If (A – C) $\subseteq$ B, then A $\subseteq$ B
Key: D
Sol:
Sol:
The question provides that $A \cap B \subseteq C$ and $A \cap B \neq \phi$. Analyzing each statement:
Statement A: If $(A - B) \subseteq C$, then $A \subseteq C$. This statement can be verified using Venn diagrams. If the part of A that is not in B is contained in C, then A is a subset of C.
Statement B: $B \cap C \neq \phi$. This means that the intersection of B and C is not empty. Given that $A\cap B \subseteq C$, this is true.
Statement C: $(C \cup A) \cap (C \cup B) = C$. Using the distributive property of sets, $(C \cup A) \cap (C \cup B) = C \cup (A \cap B)$. Since $A \cap B \subseteq C$, then $C \cup (A \cap B) = C$. So, this statement is true.
Statement D: If $(A - C) \subseteq B$, then $A \subseteq B$. This statement is NOT necessarily true. It is possible to have $A - C \subseteq B$, $A \cap B \subseteq C$ and $A \cap B \neq \phi$, but it does NOT require that $A \subseteq B$. This is because A can contain elements outside of B that are also outside of C.
Therefore, the statement that is not true is D.
#1059
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2020
JEE Main 2020 (Online) 9th January Evening Slot
KNOWLEDGE
4 Marks
If $A = {x \in R : |x| < 2}$ and $B = {x \in R : |x – 2| \geq 3}$; then :
(A) $A – B = [–1, 2)$
(B) $A \cup B = R – (2, 5)$
(C) $A \cap B = (–2, –1)$
(D) $B – A = R – (–2, 5)$
Key: D
Sol:
Sol:
Given $A = {x \in R : |x| < 2}$ and $B = {x \in R : |x – 2| \geq 3}$.
We can rewrite the sets as follows:
$A = {x \in R : -2 < x < 2} = (-2, 2)$
$B = {x \in R : x – 2 \geq 3 \text{ or } x – 2 \leq -3} = {x \in R : x \geq 5 \text{ or } x \leq -1} = (-\infty, -1] \cup [5, \infty)$
Now, we want to find $B – A$, which is the set of elements in $B$ but not in $A$.
$B – A = B \cap A^c$, where $A^c$ is the complement of $A$.
$A^c = (-\infty, -2] \cup [2, \infty)$
Then, $B – A = ((-\infty, -1] \cup [5, \infty)) \cap ((-\infty, -2] \cup [2, \infty))$
$B - A = (-\infty, -1] \cup [5, \infty) - (-2,2) = (-\infty, -1] \cup [5, \infty)$.
In other words, $B-A$ is the set of all real numbers except those in the interval $(-2, 2)$.
So, $B-A = R - (-2, 5)$.
#1058
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2020
JEE Main 2020 (Online) 2nd September Morning Slot
KNOWLEDGE
4 Marks
If $R = {(x, y) : x, y \in Z, x^2 + 3y^2 \le 8}$ is a relation on the set of integers $Z$, then the domain of $R^{-1}$ is :
(A) {0, 1}
(B) {-2, –1, 1, 2}
(C) {-1, 0, 1}
(D) {-2, –1, 0, 1, 2}
Key: C
Sol:
Sol:
Given $R = {(x, y) : x, y \in Z, x^2 + 3y^2 \le 8}$.
So $R = {(0,1), (0,-1), (1,0), (-1,0), (1,1), (1,-1), (-1,1), (-1,-1), (2,0), (-2,0), (2,1), (2,-1), (-2,1), (-2,-1)}$.
$\Rightarrow R : {-2, -1, 0, 1, 2} \rightarrow {-1, 0, 1}$.
$\therefore R^{-1} : {-1, 0, 1} \rightarrow {-2, -1, 0, 1, 2}$.
$\therefore$ Domain of $R^{-1} = {-1, 0, 1}$.
#1057
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2020
JEE Main 2020 (Online) 3rd September Morning Slot
KNOWLEDGE
4 Marks
Consider the two sets: A = {$m ∈ R$: both the roots of $x^2 – (m + 1)x + m + 4 = 0$ are real} and B = [–$3$, $5$). Which of the following is not true?
(A) A ∩ B = {–$3$}
(B) B – A = (–$3$, $5$)
(C) A ∪ B = R
(D) A - B = ($-∝$, –$3$) ∪ ($5$, $∝$)
Key: D
Sol:
Sol:
For the roots to be real, the discriminant $D ≥ 0$.
$(m+1)^2 - 4(m+4) ≥ 0$
$m^2 + 2m + 1 - 4m - 16 ≥ 0$
$m^2 - 2m - 15 ≥ 0$
$(m-5)(m+3) ≥ 0$
$m ∈ (-∞, -3] ∪ [5, ∞)$
Therefore, $A = (-∞, -3] ∪ [5, ∞)$. Given $B = [-3, 5)$.
Analyzing the options:
Option A: $A ∩ B = {-3}$. This is true since the intersection contains only $-3$.
Option B: $B – A = (-3, 5)$. This is true because removing $A$ from $B$ leaves the interval $(-3, 5)$.
Option C: $A ∪ B = R$. This is true, as the union covers all real numbers.
Option D: $A - B = (-∞, -3) ∪ (5, ∞)$. This is incorrect. $A - B$ should be $(-∞, -3) ∪ [5, ∞)$. The given interval does not include $5$.
Thus, option D is not true.
#1056
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2020
JEE Main 2020 (Online) 3rd September Evening Slot
KNOWLEDGE
4 Marks
Let $R_1$ and $R_2$ be two relation defined as follows: $R_1 = {(a, b) \in R^2 : a^2 + b^2 \in Q}$ and $R_2 = {(a, b) \in R^2 : a^2 + b^2 \notin Q}$, where $Q$ is the set of all rational numbers. Then :
(A) Neither $R_1$ nor $R_2$ is transitive.
(B) $R_2$ is transitive but $R_1$ is not transitive.
(C) $R_1$ and $R_2$ are both transitive.
(D) $R_1$ is transitive but $R_2$ is not transitive.
Key: A
Sol:
Sol:
For $R_1$: Let $a = 1 + \sqrt{2}$, $b = 1 - \sqrt{2}$, $c = \sqrt[4]{8}$. $aR_1b : a^2 + b^2 = 6 \in Q$ $bR_1c : b^2 + c^2 = 3 - 2\sqrt{2} + 2\sqrt{2} = 3 \in Q$ $aR_1c : a^2 + c^2 = 3 + 2\sqrt{2} + 2\sqrt{2} \notin Q$ $\therefore$ $R_1$ is not transitive. For $R_2$: Let $a = 1 + \sqrt{2}$, $b = \sqrt{2}$, $c = 1 - \sqrt{2}$ $aR_2b : a^2 + b^2 = 5 + 2\sqrt{2} \notin Q$ $bR_2c : b^2 + c^2 = 5 - 2\sqrt{2} \notin Q$ $aR_2c : a^2 + c^2 = 3 + 2\sqrt{2} + 3 - 2\sqrt{2} = 6 \in Q$ $\therefore$ $R_2$ is not transitive.
#1055
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2020
JEE Main 2020 (Online) 4th September Morning Slot
KNOWLEDGE
4 Marks
A survey shows that $63$% of the people in a city read newspaper A whereas $76$% read newspaper B. If $x$% of the people read both the newspapers, then a possible value of x can be:
(A) $37$
(B) $65$
(C) $29$
(D) $55$
Key: D
Sol:
Sol:
Let $A$ be the set of people who read newspaper A and $B$ be the set of people who read newspaper B. According to the problem, we have:
$|A| = 63$
$|B| = 76$
$|A \cup B| = |A| + |B| - |A \cap B|$
Also, $|A \cup B|$ represents the percentage of people who read at least one of the newspapers, and it cannot exceed $100$. We are given that $x$% of the people read both newspapers, so $|A \cap B| = x$.
Therefore, $|A \cup B| = 63 + 76 - x = 139 - x$.
Since $|A \cup B| \le 100$, we have $139 - x \le 100$, which implies $x \ge 39$.
From the Venn diagram, $x$ must be less than or equal to both $63$ and $76$. So, $x \le 63$.
Thus, $39 \le x \le 63$.
From the given options, the only value that satisfies this inequality is $55$.
Therefore, the possible value of $x$ is $55$.
#1054
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2020
JEE Main 2020 (Online) 4th September Evening Slot
KNOWLEDGE
4 Marks
Let $\bigcup_{i=1}^{50} X_i = \bigcup_{i=1}^{n} Y_i = T$ where each $X_i$ contains $10$ elements and each $Y_i$ contains $5$ elements. If each element of the set $T$ is an element of exactly $20$ of sets $X_i$'s and exactly $6$ of sets $Y_i$'s, then $n$ is equal to:
(A) $30$
(B) $50$
(C) $15$
(D) $45$
Key: A
Sol:
Sol:
$\bigcup_{i=1}^{50} X_i = X_1, X_2,....., X_{50} = 50$ sets. Given each sets having $10$ elements.
So total elements = $50 \times 10$
$\bigcup_{i=1}^{n} Y_i = Y_1, Y_2,....., Y_n = n$ sets. Given each sets having $5$ elements.
So total elements = $5 \times n$
Now each element of set $T$ contains exactly $20$ of sets $X_i$.
So number of effective elements in set $T = \frac{50 \times 10}{20}$
Also each element of set $T$ contains exactly $6$ of sets $Y_i$.
So number of effective elements in set $T = \frac{n \times 5}{6}$
$\therefore \frac{50 \times 10}{20} = \frac{n \times 5}{6}$
$\Rightarrow n = 30$
#1053
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2020
JEE Main 2020 (Online) 5th September Morning Slot
KNOWLEDGE
4 Marks
A survey shows that $73$% of the persons working in an office like coffee, whereas $65$% like tea. If $x$ denotes the percentage of them, who like both coffee and tea, then $x$ cannot be :
(A) $63$
(B) $36$
(C) $54$
(D) $38$
Key: B
Sol:
Sol:
Let C be the set of persons who like coffee and T be the set of persons who like tea. Given: $n(C) = 73$ and $n(T) = 65$. Also, $n(C \cup T) \le 100$. Using the formula for the union of two sets: $n(C \cup T) = n(C) + n(T) - n(C \cap T)$. Let $x = n(C \cap T)$ be the percentage of people who like both coffee and tea. So, $n(C \cup T) = 73 + 65 - x \le 100$. This implies $138 - x \le 100$, which gives $x \ge 38$. Also, $x$ must be less than or equal to both $73$ and $65$ since $x$ represents the intersection. So, $x \le 73$ and $x \le 65$. Therefore, $38 \le x \le 65$. Since $x$ must be in the range $[38, 65]$, the value $x=36$ is not possible.
#1052
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2021
JEE Main 2021 (Online) 26th February Morning Shift
KNOWLEDGE
4 Marks
Let $R = {(P, Q) | P$ and $Q$ are at the same distance from the origin} be a relation, then the equivalence class of $(1, −1)$ is the set :
(A) $S = {(x, y) | x^2 + y^2 = \sqrt{2}}$
(B) $S = {(x, y) | x^2 + y^2 = 2}$
(C) $S = {(x, y) | x^2 + y^2 = 1}$
(D) $S = {(x, y) | x^2 + y^2 = 4}$
Key: B
Sol:
Sol:
Given $R = {(P, Q) | P$ and $Q$ are at the same distance from the origin}.
Then the equivalence class of $(1, -1)$ will contain all such points that lie on the circumference of the circle with the center at the origin and passing through the point $(1, -1)$.
The radius of the circle $= \sqrt{1^2 + (-1)^2} = \sqrt{1 + 1} = \sqrt{2}$. Therefore, the equation of the circle is $x^2 + y^2 = (\sqrt{2})^2 = 2$.
Required equivalence class of $(S) = {(x, y) | x^2 + y^2 = 2}$.
#1051
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2021
JEE Main 2021 (Online) 16th March Morning Shift
KNOWLEDGE
4 Marks
The number of elements in the set {$x \in R : (|x| - 3) |x + 4| = 6$} is equal to :
(A) 4
(B) 2
(C) 3
(D) 1
Key: B
Sol:
Sol:
We need to consider three cases based on the value of $x$:
Case 1: $x \le -4$
In this case, $|x| = -x$ and $|x+4| = -(x+4)$. The equation becomes:
$(-x - 3)(-x - 4) = 6$
$(x + 3)(x + 4) = 6$
$x^2 + 7x + 12 = 6$
$x^2 + 7x + 6 = 0$
$(x + 1)(x + 6) = 0$
$x = -1$ or $x = -6$
Since $x \le -4$, we only accept $x = -6$.
Case 2: $-4 < x < 0$
In this case, $|x| = -x$ and $|x+4| = x+4$. The equation becomes:
$(-x - 3)(x + 4) = 6$
$-x^2 - 4x - 3x - 12 = 6$
$-x^2 - 7x - 18 = 0$
$x^2 + 7x + 18 = 0$
The discriminant is $D = 7^2 - 4(1)(18) = 49 - 72 = -23 < 0$. So, there are no real solutions in this case.
Case 3: $x \ge 0$
In this case, $|x| = x$ and $|x+4| = x+4$. The equation becomes:
$(x - 3)(x + 4) = 6$
$x^2 + 4x - 3x - 12 = 6$
$x^2 + x - 18 = 0$
Using the quadratic formula, $x = \frac{-1 \pm \sqrt{1^2 - 4(1)(-18)}}{2(1)} = \frac{-1 \pm \sqrt{1 + 72}}{2} = \frac{-1 \pm \sqrt{73}}{2}$
Since $x \ge 0$, we take the positive root: $x = \frac{-1 + \sqrt{73}}{2} \approx \frac{-1 + 8.54}{2} \approx 3.77$.
So, $x = \frac{-1 + \sqrt{73}}{2}$ is a valid solution.
Therefore, the solutions are $x = -6$ and $x = \frac{-1 + \sqrt{73}}{2}$. The number of elements in the set is 2.
#1050
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2021
JEE Main 2021 (Online) 16th March Evening Shift
KNOWLEDGE
4 Marks
Let $A = {2, 3, 4, 5, ....., 30}$ and '$\simeq$' be an equivalence relation on $A \times A$, defined by $(a, b) \simeq (c, d)$, if and only if $ad = bc$. Then the number of ordered pairs which satisfy this equivalence relation with ordered pair $(4, 3)$ is equal to :
(A) $5$
(B) $6$
(C) $8$
(D) $7$
Key: D
Sol:
Sol:
Given that $(a,b) \simeq (4,3)$, we have $3a=4b$, which means $a = \frac{4}{3}b$. Since $a$ must be an integer, $b$ must be a multiple of $3$. The possible values of $b$ are ${3, 6, 9, 12, 15, 18, 21, 24, 27, 30}$. For each value of $b$, we can find the corresponding value of $a$:
If $b=3$, $a=\frac{4}{3}(3) = 4$.
If $b=6$, $a=\frac{4}{3}(6) = 8$.
If $b=9$, $a=\frac{4}{3}(9) = 12$.
If $b=12$, $a=\frac{4}{3}(12) = 16$.
If $b=15$, $a=\frac{4}{3}(15) = 20$.
If $b=18$, $a=\frac{4}{3}(18) = 24$.
If $b=21$, $a=\frac{4}{3}(21) = 28$.
If $b=24$, $a=\frac{4}{3}(24) = 32$. But $a$ must be less than or equal to $30$, so we stop here.
If $b=27$, $a=\frac{4}{3}(27) = 36$, which is also greater than $30$.
If $b=30$, $a=\frac{4}{3}(30) = 40$, which is also greater than $30$.
The pairs $(a, b)$ that satisfy the condition are $(4, 3), (8, 6), (12, 9), (16, 12), (20, 15), (24, 18), (28, 21)$. There are $7$ such ordered pairs.
#1049
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2021
JEE Main 2021 (Online) 17th March Morning Shift
KNOWLEDGE
4 Marks
In a school, there are three types of games to be played. Some of the students play two types of games, but none play all the three games. Which Venn diagrams can justify the above statement?
(A) Q and R
(B) None of these
(C) P and R
(D) P and Q
Key: B
Sol:
Sol:
The question states that none of the students play all three games. This means that the intersection of all three sets (circles) in the Venn diagram must be empty. Observing the provided Venn diagrams (P, Q, and R), we see that in each case, there is an intersection between all three circles. Thus, none of the diagrams satisfy the condition that no student plays all three games.
Therefore, the correct answer is 'None of these'.
#1048
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2021
JEE Main 2021 (Online) 18th March Evening Shift
KNOWLEDGE
4 Marks
Define a relation $R$ over a class of $n imes n$ real matrices $A$ and $B$ as "$ARB$ iff there exists a non-singular matrix $P$ such that $PAP^{-1} = B$". Then which of the following is true?
(A) $R$ is reflexive, transitive but not symmetric
(B) $R$ is symmetric, transitive but not reflexive.
(C) $R$ is reflexive, symmetric but not transitive
(D) $R$ is an equivalence relation
Key: D
Sol:
Sol:
For reflexive relation, $\forall (A, A) \in R$ for matrix $P$. $\Rightarrow A = PAP^{-1}$ is true for $P = I$. So, $R$ is reflexive relation.
For symmetric relation, Let $(A, B) \in R$ for matrix $P$. $\Rightarrow A = PBP^{-1}$. After pre-multiply by $P^{-1}$ and post-multiply by $P$, we get $P^{-1}AP = B$. So, $(B, A) \in R$ for matrix $P^{-1}$. So, $R$ is a symmetric relation.
For transitive relation, Let $ARB$ and $BRC$. So, $A = PBP^{-1}$ and $B = PCP^{-1}$. Now, $A = P(PCP^{-1})P^{-1} \Rightarrow A = (P)^2C(P^{-1})^2 \Rightarrow A = (P)^2 \cdot C \cdot (P^2)^{-1}$. $\therefore (A, C) \in R$ for matrix $P^2$. $\therefore R$ is transitive relation. Hence, $R$ is an equivalence relation.
#1047
Mathematics
Sets, Relations, and Functions
MCQ_SINGLE
APPLY
2021
JEE Main 2021 (Online) 27th July Evening Shift
KNOWLEDGE
4 Marks
Let $N$ be the set of natural numbers and a relation $R$ on $N$ be defined by $R = {(x, y) ∈ N × N: x^3 - 3x^2y - xy^2 + 3y^3 = 0}$. Then the relation $R$ is :
(A) symmetric but neither reflexive nor transitive
(B) reflexive but neither symmetric nor transitive
(C) reflexive and symmetric, but not transitive
(D) an equivalence relation
Key: B
Sol:
Sol:
Given the relation $x^3 - 3x^2y - xy^2 + 3y^3 = 0$. We can factor this as follows:
$x(x^2 - y^2) - 3y(x^2 - y^2) = 0$
$(x - 3y)(x^2 - y^2) = 0$
$(x - 3y)(x - y)(x + y) = 0$
Thus, the relation holds if $x = 3y$, $x = y$, or $x = -y$.
Reflexivity: For $R$ to be reflexive, $(x, x) \in R$ for all $x \in N$. If $x = y$, then $(x, x) \in R$. So, the relation is reflexive.
Symmetry: For $R$ to be symmetric, if $(x, y) \in R$, then $(y, x) \in R$. Let's consider $x = 3y$. If $(3, 1) \in R$ since $3 = 3(1)$, but $(1, 3) \notin R$ since $1 \neq 3(3)$. So, the relation is not symmetric.
Transitivity: For $R$ to be transitive, if $(x, y) \in R$ and $(y, z) \in R$, then $(x, z) \in R$. Let $x = 3y$ and $y = z$. Then $(x, y) = (3y, y)$ and $(y, z) = (y, y)$. For transitivity, we need $(3y, y) \in R$ and $(y, y) \in R$ implying $(3y, y) \in R$. However, if we choose $x=3$, $y=1$ and $z=1$, then $x = 3y$. But if $x = 3$ and $y = 1$, we don't have $x=z$. So the relation is not transitive.
Since $R$ is reflexive but neither symmetric nor transitive, the correct option is B.