Official Guide Explanation:
Data Sufficiency #86

Background

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Solution and Metadata

Question: 86
Page: 159
Difficulty: 5 (Moderate)
Category 1: Arithmetic > Properties of Integers > Other
Category 2: Arithmetic > Properties of Integers > Evens and Odds

Explanation: If m and n are consecutive positive integers, there are two possible scenarios: m is greater than n (as in m = 3 and n = 2) and n is greater than m (as in m = 2 and n = 3).

Statement (1) is sufficient: if m - 1 and n + 1 are consecutive, we can check the two scenarios above to see if both of them work. If m = 3 and n = 2, m - 1 = 2 and n + 1 = 3, which are consecutive integers, so it is possible that m is greater than n. If m = 2 and n = 3, m - 1 = 1 and n + 1 = 4, which are not consecutive integers. Thus, m must be greater than n.

Statement (2) is insufficient: if m = 2, n could be either 1 or 3: greater than or less than m. Choice (A) is correct.

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