Official Guide Explanation:
Data Sufficiency #13




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Solution and Metadata

Question: 13
Page: 273
Difficulty: 3 (Very Easy)
Category 1: Algebra > Linear Equations-One Unk >
Category 2: Word Problems > Other >

Explanation: First, simplify the information given. The first three minutes, at 42 cents per minute, costs a total of $1.26. The total cost of the call can be given as:

1.26 + 0.18(a)

where a is the number of additional minutes. Alternatively, since the number of "additional minutes" is 3 minutes less than the length of the call, we can use this:

1.26 + 0.18(m - 3)

where m is the total number of minutes of the call.

Statement (1) is sufficient. We know that the first three minutes cost $1.26. If that's 36 cents less than the cost of the remainder of the call, the remainder of the call cost:

$1.26 + $0.36 = $1.62.

We can divide that number by 18 cents to determine the number of additional minutes.

Statement (2) is also sufficient. Using the formula we derived from the question:

1.26 + 0.18(m - 3) = 2.88

Here, we have only one variable in a linear equation, so we have enough information to solve. At this point you can conclude that (D) is the correct answer. To solve it for good measure:

1.26 + 0.18(m - 3) = 2.88

0.18(m - 3) = 1.62

m - 3 = 9

m = 12

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