Official Guide Explanation:
Data Sufficiency #126

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Solution and Metadata

Question: 126
Page: 284
Difficulty: 5 (Moderate)
Category 1: Word Problems > Sets >
Category 2: Arithmetic > Sets > 2 sets

Explanation: Statement (1) is not sufficient: if 20 of the 60 cars had a stereo but no power windows, then 40 of the cars either had both, neither, or power windows but no stereo. Statement (2) is also not sufficient: if 30 of the 60 cars had both, that leaves 30 cars that either had stereo but no power windows, power windows but no stereo, or neither.

Taken together, it's still not enough information. Given what we know about 50 of the 60 cars, that leaves 10 cars that either have power windows but no stereo, or neither. Without knowing how many cars have power windows but not stereo, it's insufficient, choice (E).

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