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Que: The cost of a certain phone call was $2 for the first 2 minutes and $0.10 for.......

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Que: The cost of a certain phone call was $2 for the first 2 minutes and $0.10 for.......

by Max@Math Revolution » Fri Jun 25, 2021 9:05 pm

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Que: The cost of a certain phone call was $2 for the first 2 minutes and $0.10 for each additional minute after the first 2 minutes. Did the phone call last longer than 10 minutes?

(1) The cost of the phone call was less than $3.00.
(2) The cost of the phone call was greater than $3.00.
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Source: — Data Sufficiency |
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Re: Que: The cost of a certain phone call was $2 for the first 2 minutes and $0.10 for.......

by Max@Math Revolution » Sun Jun 27, 2021 8:03 pm

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Solution: To save time and improve accuracy on DS questions in GMAT, learn and apply the Variable Approach.

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

Visit https://www.mathrevolution.com/gmat/lesson for details.

Now we will solve this DS question using the Variable Approach.

Let’s apply the 3 steps suggested previously.

Follow the first step of the Variable Approach by modifying and rechecking the original condition and the question.

We have to find whether the call cost longer than 10 minutes.

A 10- minute call will cost as: cost of 2 minutes + cost of 8 minutes = $2 + 8($0.10) = $2.80

We have to find did the call cost more than $2.80?

Condition (1) tells us that the cost of the phone call was less than $3.00.

If call cost = $2.70, then we get NO as an answer.
But If call cost = $2.90, then we get YES as an answer.

The answer is not a unique YES or a NO; condition (1) alone is not sufficient according to Common Mistake Type 1 which states that the answer should be a unique YES or a NO.

Condition (2) tells us that the cost of the phone call was greater than $3.00.

This implies that the cost of the call will always be greater than $2.80 - YES

The answer is a unique YES; condition (2) alone is sufficient according to Common Mistake Type 1 which states that the answer should be a unique YES or a NO.

Condition (2) alone is sufficient.

Therefore, B is the correct answer.

Answer: B
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