Let X = {3, 6, 12, 24, 48}. Let <= be the partial order defined by X <= Y if X divides Y. Number of edges in the Hasse diagram of (X, <=) is A. 3 B. 4 C. 9 D. None of the above
GATE 1996 · Discrete Mathematics · Partial Order · medium
Answer: B. 4
- Identify all covering pairs: (3,6): 3|6, no z in X with 3|z|6 - cover. (6,12): 6|12, no intermediate z - cover. (12,24): 12|24, no intermediate - cover. (24,48): 24|48, no intermediate - cover. Non-consecutive: (3,12) has 6 between; (6,24) has 12; (12,48) has 24; etc. - all non-covers.
- Count edges: Covering pairs: (3,6), (6,12), (12,24), (24,48) = 4 edges. A chain of 5 elements has 5 - 1 = 4 Hasse diagram edges. Answer is B.