Official Guide Explanation:
Data Sufficiency #55

Background

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Solution and Metadata

Question: 55
Page: 157
Difficulty: 6 (Moderately Difficult)
Category 1: Word Problems > Rate Problems > Speed
Category 2: Arithmetic > Fractions >

Explanation: To find the time the machine finished filling the order, you need to know what time it started, and how it took to fill the order. Statement (1) is insufficient: there's no indication of how long it took to fill the order.

Statement (2) is sufficient: it indicates that (5/6) - (1/2) = (1/3) of the order could be completed in 40 minutes, which means that the whole order took 40(3) = 120 minutes. Since it was half finished at 10:30 and filling half the order took (120/2) = 60 minutes, it must have started at 9:30, which means it finished at 12:30. Choice (B) is correct.

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