Data Sufficiency

Que: The cost of a certain phone call was $3 for the first 4 minutes and $0.20 for each additional minute after the first 4 minutes. Did the phone call last longer than 8 minutes?

(1) The cost of the phone call was greater than $5.00.
(2) The cost of the phone call was less than $5.00.

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.

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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 8 minutes.

A 8- minute call will cost as: cost of 4 minutes + additional cost of 4 minutes = $3 + 4($0.20) = $3.80

We have to find did the call cost more than $3.80?

Condition (1) tells us that the cost of the phone call was more than $5.00.

This implies the cost of the call will always be greater than $3.80 - YES

The answer is a unique YES; condition (1) alone is 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 less than $5.00.

=> If call cost = $2.70, then we get NO as an answer

=> But If call cost = $4.00, then we get YES as an answer

The answer is not a unique YES or a NO; condition (2) alone is not sufficient according to Common Mistake Type 1 which states that the answer should be a unique YES or a NO.

Condition (1) alone is sufficient.

Therefore, A is the correct answer.

Answer: A