Official Guide Explanation:
Data Sufficiency #95




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Solution and Metadata

Question: 95
Page: 281
Difficulty: 5 (Moderate)
Category 1: Algebra > Linear Equations-Two Unk >
Category 2: Arithmetic > Real Numbers >

Explanation: Statement (1) is insufficient. If rs = 1, rst will be 1 if t equals 1. Since we don't know whether t is 1, we don't know whether rst = 1. Statement (2) is also insufficient: if st = 1, rst will be 1 if r is 1. Since we don't know whether r is 1, we don't know whether rst = 1.

Taken together, the statements are still insufficient. rs = 1 and st = 1, which means that r = t. So, we can put all three variables in terms of r: s = (1/(r)), and t = r. We can then rewrite the question: is (r)((1/(r)))(r) = 1, or "Is r = 1?" Neither statement says anything about a specific variable, so we don't know. The correct choice is (E).

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