Solution: To save time and improve accuracy on DS question in GMAT, learn, and apply a 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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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 a ‘value of 14 # 7’ where ‘#’ represents addition, subtraction, multiplication, or division.
Follow the second and the third step: From the original condition, we have 1 variable (#). To match the number of variables with the number of equations, we need 1 equation. Since conditions (1) and (2) will provide 1 equation each, D would most likely be the answer.
Recall 3- Principles and Choose D as the most likely answer. Let’s look at each condition separately.
Condition (1) tells us that 25 # 5 = 5, from which we get # = division, since 25 / 5 = 5.
Then 14 # 7: 14 / 7 = 2 which is a unique answer.
The answer is unique and condition (1) alone is sufficient according to Common Mistake Type 2 which states that the answer should be a unique value.
Condition (2) tells us that 2#1 = 2, from which we get # can be multiplication or division.
If # = multiplication, then 2 * 1 = 2,
=> Then 14 # 7: 14 * 7 = 98
But if # = division, then 2/ 1 = 2,
=> Then 14 # 7: 14 / 7 = 2
The answer is not a unique value and condition (2) alone is not sufficient according to Common Mistake Type 2 which states that the answer should be a unique value.
Condition (1) alone is sufficient.
Therefore, A is the correct answer.
Answer: A
