Class JEE Mathematics Sets, Relations, and Functions Q #1019
KNOWLEDGE BASED
APPLY
4 Marks 2024 JEE Main 2024 (Online) 4th April Evening Shift MCQ SINGLE
Let a relation $R$ on $N \times N$ be defined as: $(x_1, y_1) R (x_2, y_2)$ if and only if $x_1 \le x_2$ or $y_1 \le y_2$. Consider the two statements:
(I) $R$ is reflexive but not symmetric.
(II) $R$ is transitive
Then which one of the following is true?
(A) Only (II) is correct.
(B) Both (I) and (II) are correct.
(C) Neither (I) nor (II) is correct.
(D) Only (I) is correct.
Correct Answer: D
Explanation
Given the relation $(x_1, y_1) R (x_2, y_2)$ if $x_1 \le x_2$ or $y_1 \le y_2$.
For reflexivity, we need to check if $(x_1, y_1) R (x_1, y_1)$.
Since $x_1 \le x_1$ and $y_1 \le y_1$, the condition $x_1 \le x_1$ or $y_1 \le y_1$ is true. Therefore, $R$ is reflexive.
For symmetry, if $(x_1, y_1) R (x_2, y_2)$, then $x_1 \le x_2$ or $y_1 \le y_2$. For $R$ to be symmetric, $(x_2, y_2) R (x_1, y_1)$ must also be true, which means $x_2 \le x_1$ or $y_2 \le y_1$. This is not necessarily true. For example, $(1, 2) R (3, 4)$ since $1 \le 3$ or $2 \le 4$, but $(3, 4) R (1, 2)$ is false because neither $3 \le 1$ nor $4 \le 2$ is true. Thus, $R$ is not symmetric.
For transitivity, consider pairs $(3, 9)$, $(4, 6)$, and $(2, 7)$.
$(3, 9) R (4, 6)$ because $3 \le 4$.
$(4, 6) R (2, 7)$ because $6 \le 7$.
However, $(3, 9) R (2, 7)$ is false because neither $3 \le 2$ nor $9 \le 7$ is true. Therefore, $R$ is not transitive.
Since $R$ is reflexive but not symmetric, statement (I) is correct.
Since $R$ is not transitive, statement (II) is incorrect.
Thus, only statement (I) is correct.

More from this Chapter

NUMERICAL
Let S = {1, 2, 3, 5, 7, 10, 11}. The number of non-empty subsets of S that have the sum of all elements a multiple of 3, is _____________.
MCQ_SINGLE
Let $A = {1, 2, 3, ..., 100}$ and $R$ be a relation on $A$ such that $R = {(a, b) : a = 2b + 1}$. Let $(a_1, a_2), (a_2, a_3), (a_3, a_4), ..., (a_k, a_{k+1})$ 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 :
NUMERICAL
Let X = {n $ \in $ N : 1 $ \le $ n $ \le $ 50}. If A = {n $ \in $ X: n is a multiple of 2} and B = {n $ \in $ X: n is a multiple of 7}, then the number of elements in the smallest subset of X containing both A and B is ________.
NUMERICAL
Let $S=\left\{p_1, p_2 \ldots, p_{10}\right\}$ be the set of first ten prime numbers. Let $A=S \cup P$, where $P$ is the set of all possible products of distinct elements of $S$. Then the number of all ordered pairs $(x, y), x \in S$, $y \in A$, such that $x$ divides $y$, is ________ .
NUMERICAL
In a survey of 220 students of a higher secondary school, it was found that at least 125 and at most 130 students studied Mathematics; at least 85 and at most 95 studied Physics; at least 75 and at most 90 studied Chemistry; 30 studied both Physics and Chemistry; 50 studied both Chemistry and Mathematics; 40 studied both Mathematics and Physics and 10 studied none of these subjects. Let $m$ and $n$ respectively be the least and the most number of students who studied all the three subjects. Then $\mathrm{m}+\mathrm{n}$ is equal to ___________.
View All Questions