Effective vs. Efficient on the GMAT

Two words that often get confused in the English language are effective and efficient. Many people use these words as if they are synonyms, when, in fact, they are two distinct notions that only sound like homonyms. In fact, the words effective and efficient complement each other perfectly.  How does this affect the GMAT? While both words are usually used as compliments, their effect on the exam is very noticeable (see what I did there?)

Efficient is a buzz word that gets thrown around a lot in the corporate world. It’s usually accompanied by “streamline” and “right-size”. In a nutshell, it means that you get to the answer quickly, although that answer could still be faulty.

Effective is a word with many meanings, but in this context I’m going to concentrate on the definition about getting the desired result. A solution is effective if it gets you the right result, and it’s efficient if you get there in a reasonable amount of time. As you can imagine, you’re aiming for both at all times.

Much like in data sufficiency, you can probably tell how having both of these terms together gives you all the information you need. Being efficient means you took 45 seconds to get the right answer, but it’s kind of moot if you picked the wrong one. You may as well have just taken a blind stab at it. Effective means you got the right answer, but if it took you 6 minutes your overall GMAT score will undoubtedly be lower than you’d hoped for.

On the GMAT, you must be both effective and efficient. However, this type of advice is tantamount to saying: “Get all the questions right” (easy in theory, kind of a mess in practice). On the exam, you’re likely to have fairly straight forward questions that you can certainly get right, but that might take you too long without some kind of strategy. In other words, you can be effective, but you can’t necessarily be efficient. How do I get these two terms on the same page? By using logic and deductive reasoning, coincidentally the two most important concepts on the GMAT (who’da thunk it?)

Consider the question below:

A student’s average (arithmetic mean) test score on 4 tests is 78. What must be the student’s score on a 5th test for the student’s average score on the 5 tests to be 80?

  1. 80

  2. 82

  3. 84

  4. 86

  5. 88

Clearly with a calculator, this question is borderline trivial. I have all the information I need, and in fact I could just methodically run through each answer choice in the formula: 80 + 80 + 80 + 80 + 80 = 78 + 78 + 78 + 78 + N. This strategy will be effective; however, there are more efficient ways to get the right answer here.

The first alternative is to use the notion of the sum. If these two series of 5 numbers summed up to the same number, they would necessarily have the same average. The hypothetical series is 5 x 80, which has a product of 400. The actual series has a total of 4 x 78 + N, but it has to end up with the same 400 at the end of the day. Multiplying 78 x 4 isn’t trivial, but you can get 312 within a few seconds with or without paper. This leaves 400 – 312 = 88 points to get on the fifth exam (N). This method works well but requires some relatively cumbersome math that could easily lead to a distracted error. Can we use the same principle more efficiently? (Hint: the answer will be yes!)

What if I took the notion of average instead of the sum? The hypothetical series has 5 terms, each of which is 80. The actual sum has 4 terms, the average of which is 78. This is the equivalent of having 4 tests of 78 each, meaning that each of these 4 tests is missing 2 points in order to hit the vaunted 80 threshold. Once we know we owe 8 points, the final test score must be the average + the sum of the missing points, totalling 88. This is the same principle, but it’s more efficient, and will save you time on the exam. (Much like Geiko, 15 minutes could save you 15% or more)

The GMAT is a test that requires mental agility and flexibility. If you can solve a question multiple ways, you will never be stuck looking for the correct solution. The flip side of that argument is that, if you have multiple approaches to solving a question, how do you choose among them? (Eeny meeny miny moe?) The best answer is that you go with the technique that is most effective first and most efficient second. Getting the correct answer in one minute is better than getting the correct answer in two minutes; however both are better than getting the incorrect answer in 45 seconds. Once you’ve practiced getting the right answer to the question and being effective, the next step is to hone your skills being efficient.

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Ron Awad is a GMAT instructor for Veritas Prep based in Montreal, bringing you weekly advice for success on your exam.  After graduating from McGill and receiving his MBA from Concordia, Ron started teaching GMAT prep and his Veritas Prep students have given him rave reviews ever since.