Question

Let \( A = \{1, 2, 3, \ldots, 100\} \). Let \( R \) be a relation on \( A \) defined by \( (x, y) \in R \) if and only if \( 2x = 3y \). Let \( R_1 \) be a symmetric relation on \( A \) such that \( R \subset R_1 \) and the number of elements in \( R_1 \) is \( n \). Then, the minimum value of \( n \) is \(\_\_\_\_\_\).

Answer 1

Correct Answer: 66

The relation \( R \) consists of ordered pairs \( (x, y) \) such that \( 2x = 3y \). For \( x \) and \( y \) to satisfy this relation, \( x \) and \( y \) must form pairs with specific integer values that satisfy \( 2x = 3y \).

Thus, the pairs in \( R \) are:

\[ R = \{(3, 2), (6, 4), (9, 6), (12, 8), \ldots, (99, 66)\}. \]

There are 33 such pairs in \( R \), so:

\[ n(R) = 33. \]

To make \( R_1 \) symmetric, we include both \( (x, y) \) and \( (y, x) \) for each pair in \( R \). Thus, the pairs in \( R_1 \) are:

\[ R_1 = \{(3, 2), (2, 3), (6, 4), (4, 6), (9, 6), (6, 9), \ldots, (99, 66), (66, 99)\}. \]

This doubles the number of elements:

\[ n = 2 \times 33 = 66. \]

Therefore, the minimum value of \( n \) is: \[ 66 \]