Official Guide Explanation:
Data Sufficiency #65

Background

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Solution and Metadata

Question: 65
Page: 278
Difficulty: 5 (Moderate)
Category 1: Arithmetic > Real Numbers >
Category 2: Arithmetic > Properties of Integers > Other

Explanation: When you subtract one integer from another, the result is one greater than the number of integers between them. (For instance, the difference between 4 and 2 is 2, but there's only one integer between them.) In this case, we're looking for the number of integers between r and s, which means we need the difference, from which we can subtract 1.

Statement (1) gives us the difference, so it's sufficient. Statement (2) gives us the number of integers between r + 1 and s + 1, which is the same as the number of integers between r and s. After all, the difference between r + 1 and s + 1 is the same as the difference between r and s, and the number of integers between them is always 1 less than the difference. Choice (D) is correct.

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