GMAT Tip of the Week

GMAT prep
Enough is Enough

(This is one of a series of GMAT tips that we offer on our blog.)

There are less than three weeks left in the yet-to-be-properly-named decade (The Oughts? The Double-Zeroes?), and you may be reflecting back on your progress in life since that last time we were able to heed Prince’s famed words and party in 1999. Or, as John Lennon may urge you to think, so, this is Christmas, and what have you done?

We tend to approach milestone dates and turns of the calendar with a sense of incredible ambition, and in many cases set ourselves up for disappointment. Perhaps Conan O’Brien captures this sentiment best with his “In The Year 2000…” sketches — we so often look in to the future, think we have unlimited time, and create an impossible-to-reach vision of what the future should hold, only to be disappointed in the end.

GMAT questions often offer a similar opportunity for one to get caught up in his endless ambition. A question may (seemingly) ask you to perform a calculation that is almost doable, but could be so time-consuming and fraught with opportunity for error that conducting the calculation is a fool’s mission. Consider a question such as:

What is the unit’s digit of 2^28?

An astute test taker, you may recognize that, if only the unit’s digit matters, you’re really only being asked to multiply by 2 twenty-seven times, and that, therefore, you could do the calculation in two minutes or less. However, you’ll be better served if you realize that, even after multiplying a few times, you can be satisfied with what you have. Consider that:

2^1 = 2
2^2 = 4
2^3 = 8
2^4 -> 6 (only the unit’s digit matters)
2^5 -> 2
and so on…

Once you realize that this sequence will repeat as a series of 4 (the last unique term in the set is 6, which is the fourth unique term, and then the series repeats), you can stop, and simply determine where in the sequence 2^28 will be. Because 28 is a multiple of 4, and we know that a 4-term sequence will give us the fourth term every fourth time, we know that the answer is 6.

Other GMAT questions also afford opportunities to curb your ambition and determine when you have enough to get by. Often the answer choices are far enough apart that you can stop your calculations when you simply know you’ll fall within a certain range. Or, you may find that the correct answer simply must be odd (or even), or begin/end with a certain digit, and at that point you can arrive at your answer without plugging away through every last calculation. After all, the GMAT is a management test as much as (or more than) it is a math test, so your ability to test efficiently is just as important as your need to be thorough.

Here’s to a decade of success as an MBA student and graduate!

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