Class JEE Mathematics Practice Q #961
COMPETENCY BASED
APPLY
Marks MCQ SINGLE
Let A = {-2, -1, 0, 1, 2, 3}. Let R be a relation on A defined by Ry if and only if y = max{x, 1}. Let I 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) 11
(B) 12
(C) 14
(D) 13
Correct Answer: B

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Step-by-Step Solution

Step 1: Determine the elements of relation R.

The relation R is defined by Ry if and only if y = max{x, 1}. We need to find all pairs (x, y) such that x ∈ A, y ∈ A, and y = max{x, 1}.

  • If x = -2, y = max{-2, 1} = 1. So, (-2, 1) ∈ R.
  • If x = -1, y = max{-1, 1} = 1. So, (-1, 1) ∈ R.
  • If x = 0, y = max{0, 1} = 1. So, (0, 1) ∈ R.
  • If x = 1, y = max{1, 1} = 1. So, (1, 1) ∈ R.
  • If x = 2, y = max{2, 1} = 2. So, (2, 2) ∈ R.
  • If x = 3, y = max{3, 1} = 3. So, (3, 3) ∈ R.

Therefore, R = {(-2, 1), (-1, 1), (0, 1), (1, 1), (2, 2), (3, 3)}.

Step 2: Find the number of elements in R (l).

The number of elements in R is l = 6.

Step 3: Determine the minimum number of elements to add to make R reflexive (m).

For R to be reflexive, it must contain (x, x) for all x ∈ A. A = {-2, -1, 0, 1, 2, 3}.

R already contains (1, 1), (2, 2), and (3, 3). We need to add (-2, -2), (-1, -1), and (0, 0) to make it reflexive.

So, m = 3.

Step 4: Determine the minimum number of elements to add to make R symmetric (n).

For R to be symmetric, if (x, y) ∈ R, then (y, x) ∈ R.

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

  • (-2, 1) ∈ R, so we need (1, -2).
  • (-1, 1) ∈ R, so we need (1, -1).
  • (0, 1) ∈ R, so we need (1, 0).
  • (1, 1) ∈ R, which is symmetric.
  • (2, 2) ∈ R, which is symmetric.
  • (3, 3) ∈ R, which is symmetric.

So, we need to add (1, -2), (1, -1), and (1, 0). Therefore, n = 3.

Step 5: Calculate l + m + n.

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

Correct Answer: 12

AI Suggestion: Option B

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student needs to apply the definitions of relations (reflexive, symmetric) and the max function to a given set and relation to find the values of l, m, and n, and then sum them.
Knowledge Dimension: CONCEPTUAL
Justification: The question requires understanding the concepts of relations, reflexive relations, symmetric relations, and the max function. It's not just about recalling facts but applying these concepts to a specific example.
Syllabus Audit: In the context of JEE, this is classified as COMPETENCY. The question assesses the student's ability to apply the definitions of reflexive and symmetric relations in a non-standard problem, requiring more than just recalling definitions from the textbook.