Official Guide Explanation:
Data Sufficiency #D27

Background

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Solution and Metadata

Question: D27
Page: 24
Difficulty: 4 (Moderately Easy)
Category 1: Word Problems > Other >

Explanation: Statement (1) is insufficient. We know the total charge, but that could be 1 minute for $6.50 per minute, 65 minutes for 10 cents per minute, or a variety of other options.

Statement (2) is also insufficient. We don't know the total charge, so the first - minute and additional - minute charges could be anything.

Taken together, the statements are still insufficient. One way to think about this algebraically is that she is charged the same amount (d dollars) for each of m minutes and she is also charged a $0.50 surcharge for the first minute:

md + $0.50 = $6.50

md = $6.00

Since we don't know how many minutes, or how many dollars per minute, we can't get very far with that equation. Choice (E) is correct.

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