Let A=\1, 2, 3, , 100\. Let R be a relation on A defined by (x, y) R if and only if 2x=3y. Let R1 be a symmetric relation on A such that R R1 and the number of elements in R1 is n. Then, the minimum value of n is .
Answer
66
Solution
2x=3y y=2k, x=3k with 3k 100 k=1, 2, , 33
R=\(3, 2), (6, 4), , (99, 66)\ n(R)=33
Smallest symmetric R1 R: add each reverse pair (2k, 3k) — 33 new pairs (none of them is in R, since x y)
n =33+33=66
Answer: 66