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Notice, I didn't even get involved with calculations beyond what would be on a single-digit times table, and it was enough to isolate D as the answer.
Plugging-in Values
If the answer choices are all numbers, one possible strategy is to backsolve. If the answer choices are in terms of variables, you can use algebra to solve the problem in a “forward” manner, or you can choose numbers for the variables in both the question and in the answer choices, and solve it as a numerical problem.
Let's say there are three variables in the problem. As a general rule, it's a good idea to pick a different prime number for each variable. Always avoid 1 as a plug-in value, because if z = 1, then y and yz^2 have identical values. If two of the answer choices equal each other for certain plug-in values, that's a good sign to choose different plug in values.
Solution Behavior
This is GMAC's own term for a particular strategy. Suppose you can't solve a problem to completion, but you have done enough work to eliminate two or three answers as incorrect. If you guess
randomly from among the remaining answers after having eliminated some as impossible, that is called “solution behavior.”
If you guess random from all five answers, on average this will not increase your score: the wrong answers will neatly cancel the few right answers. BUT, if you can eliminate even only one answer, this increases your odds of coming out ahead in points when you guess from the remaining answers.
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The more answers you can eliminate, the more likely you are to gain points by randomly guessing from among the remaining answers. This may be anti-intuitive, but it is borne out by careful probabilistic analysis.
It's very important to recognize: even if you can't solve a question, as long as you can intelligently eliminate some of the answer choices, you are working toward an increased score on the GMAT.
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Practice Question
Try this question online and watch the video explanation:http://gmat.magoosh.com/questions/26
Probably, out of all the math you have done in your entire pre-GMAT life, the goal has been to find the answer. In grade school math, high school math, and introductory college mathematics, you are tested and graded on your ability to find the specific numerical answer to a question. If you happened to have gotten any advanced degrees in mathematics, you know that the find-the-answer mentality as well as numbers in general quickly recede as you ascend into the realms of higher mathematics.
For the vast majority of people, though, all of us who did not choose to get college or graduate degrees in abstract mathematics, the last math that we learned prior to encountering GMAT studies in all likelihood still revolved around find-the-answer.
Data Sufficiency: Beyond “find the answer”
GMAT Data Sufficiency requires you shift your paradigm. Fundamentally, in the Data Sufficiency questions, unlike in your previous math classes, you are not being asked to find the answer. Rather, you are simply being asked the question: do you have enough information to answer the
question? In other words, if you wanted to, or had to, figure out the answer, would you have enough information to do so?
Data Sufficiency and the Managerial Mindset
Why does the GMAT ask Data Sufficiency questions? First of all, Data Sufficiency tests your ability to gauge relevance – if I want to know A, is it relevant to know B? It certainly conceivable that, in the real business world, if you want to know the price or cost or value of one thing, it will be important to be able to figure out whether knowing the price or cost or value of another thing would be relevant.
At a deeper level, think of the difference of these two questions: (1) what is the actual answer to problem X? vs. (2) do we have enough information to answer problem X? The first question may involve specific expertise, depending on the nature of the problem, and may well be delegated to, for example, an engineer. The second question is more quintessentially the manager’s question, the manager who sees that the problem can be solved and delegates it appropriately.
Insofar as you are planning to take a GMAT and go to business school, you are planning a career as a manager, which is all about delegating, about decision-making, about discerning what paths are fruitful for exploration and what paths don’t merit examination. In this sense, I would argue that GMAT Data Sufficiency tests skills that are at the very heart of what it is to be a powerful and effective manager.