Data Sufficiency

[GMAT math practice question]

The parabola y = f(x) = a(x-h)^2+k lies in the x-y plane. What is the value of k?

1) y = f(x) passes through (1,0) and (3,0).
2) y = f(x) passes through (2,1) and no y-value is greater than 1.

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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.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.



The question asks for the minimum or maximum value for the function.
Condition 2 is sufficient since it provides the maximum value for the function.

Condition 1)



The parabolas drawn above both pass through the points (1,0) and (3,0). It is obvious that we don't have a unique maximum or minimum function value. Condition 1) is not sufficient.

Therefore, B is the answer.
Answer: B