GMAT Problem Solving: There Can Be Only One

September 4, 2012 by

On the GMAT, there is only one correct answer to each question (How many caught the Highlander reference in the title?  Be honest!).

I know, big surprise, right?

But that simple, obvious statement leads us to a powerful deduction. Some Problem Solving questions on the Quantitative section will have terms, variables, or unknowns that are unsolvable—they could take multiple values on the basis of the information in the stem. And we’re not talking Data Sufficiency here. “Not sufficient” isn’t a choice (Occasionally, “Cannot be determined” is a choice on problem solving questions. This answer is usually a trap, but you can use Data Sufficiency solving techniques to see if multiple answers are possible). So if the answer choices are numbers or proportions, and some term in the question stem is unsolvable, that undetermined x-factor can’t affect the outcome. Some ratio or mathematical step in the solution has to … Read full post

GMAT Geometry: Central Angles

June 28, 2012 by

In poetry, a rose is a rose is a rose. On GMAT problems with central angle “slices” in circles, a fraction is a fraction is a fraction.

This may seem like common sense. Cut a pizza into six slices. If you cut it evenly, each slice now has one-sixth the cheese, one sixth the crust, and an angle of one sixth the way around a circle—that is, 60 degrees.  However, though this may seem obvious, it’s actually a very useful technique for resolving certain geometry problems.

Consider the following Data Sufficiency question:

In a radius 6 circle, two points A and B are connected to the center, point O. What is angle AOB?

1)    The length of the minor arc defined by sector O is 1.5π

2)    The area of the sector defined by angle AOB is 4.5π

It looks all GMAT-like and formal, but if you … Read full post

GMAT Quant: Not Revolutionary – Just Radical

June 7, 2012 by

One of the most common mistakes that I see students make when practicing for the GMAT is the misapplication of the rules that govern square roots.  When approaching a question that involves radicals, it is vital that you know not only the rules that you must follow, but also the operations that are commonly believed to be rules, but are not.  On test day, the wrong answer choices will almost always be derived from the latter.

If you need to manipulate a square root, you must remember two key rules.  First, that √(ab) = √a x √b and, second, that the √(a/b) = √a/√b.  For example, if you need to simplify √20, you can rewrite it as √(4×5).  When choosing which factors to use, always look for perfect squares.  Since 4×5 includes the perfect square 4, it is better than 2×10, which does not include a perfect … Read full post

GMAT Data Sufficiency: Say Yes, Saying No

May 21, 2012 by

The trickiest question type in the quantitative section of the GMAT for most students is yes/no data sufficiency questions.  When approaching these problems, it is imperative that you keep in mind the purpose of data sufficiency.

Let’s start with a review of data sufficiency.  On these questions, your goal is not to find the answer.  Rather, it is to determine if you have enough information to find the answer, regardless of what the answer is.  On value questions, this is fairly straightforward.  If you are asked for the value of x and you know it is 4, that’s sufficient, but if it could be 4 or 6, that’s not sufficient.  In the former case we could narrow down the possibilities to one answer.  In the latter, we could not.

Now let’s see how this same concept applies to yes/no questions.  If a question asks us if x is positive and … Read full post

When Time is not on your Side during the GMAT

February 16, 2012 by

It is essential to remember that the GMAT is about more than just doing the math correctly.  The GMAT is really a test of your critical thinking abilities – that is, your ability to not just do the work, but to figure out exactly what that work is.

To that end, the GMAT will often present you with problems that would take too long to solve if you do all of the math that is possible.  I have had countless students approach me to tell me that if they were not timed, they could solve all of the math questions.  However, they just cannot find a way to complete the problems in time.  Additionally, all the extra math provides opportunities for careless errors.  I always tell these students the same thing – do only the math you absolutely need to in order to reach the correct answer.

This is especially … Read full post

December 10, 2011 by

I’ve got a new crop of eager test-preppers just starting out on their road to GMAT success.  Often, my classes will contain one or two folks with at least some prior GMAT experience, but this group is all green and it’s gonna be fun.  However, before the fun can really get rolling I have to spend time drawing blood.

Many of the battles I must wage (and win) in the GMAT classroom are focused on preconceptions.  Whether a student has GMAT history or is coming in blind, all will inevitably have several strongly held beliefs about the test and everything that comes along with it, including their ability to crack it.  Sometimes, these beliefs will be their most significant road block on the way to hitting their target.

After last night’s class, a student stayed behind for some clarification on Data Sufficiency questions.  This student—let’s call her Jane—believes that … Read full post

Kaplan GMAT Sample Problem: Data Sufficiency Averages

August 3, 2011 by

GMAT Data Sufficiency questions can take simple concepts like averages and have test-takers pausing or falling into traps because of the way they are worded, and the fact that you have to keep in mind what your goal is with Data Sufficiency—to find out whether or not you have sufficient information to answer the question!

Problem:

Each of the 8 numbers s, t, u, v, w, x, y and z is positive.  Is the average (arithmetic mean) of s, t, u, v, w, x, y and z greater than 46?

(1) The average (arithmetic mean) of s, t, u, v and w is greater than 74.

(2) The average of x, y and z is greater than 120.

Solution:

Before evaluating the statements, you should reword the question.  We are asked if the average of a list of numbers is greater than 46.  Since average is equal to the … Read full post

Paraphrasing on GMAT Data Sufficiency Questions

August 1, 2011 by

Math on the GMAT can be hard enough when it is presented without trickery. However, the test-maker knows that even simple math can be made challenging by including complex verbal descriptions or by disguising one mathematical concept as another. Kaplan considers paraphrasing one of the core competencies necessary to crack the GMAT, and this is never more true then when you are approaching complex Data Sufficiency question stems.

At the most basic level, you should ‘paraphrase’ any algebraic word problems in DS question stems as mathematical equations. Consider the following DS stem:

Prior to a reorganization, every manager in a company supervised 17 workers. Under the new company structure, several new managers were hired, and each manager now supervises 14 workers. If the number of workers did not change, how many managers were there after the reorganization?

Inexperienced and overeager test-takers … Read full post

Kaplan GMAT Sample Question: Data Sufficiency Multiples

June 27, 2011 by

Try this GMAT Data Sufficiency question dealing with multiples and divisibility.  Remember on Data Sufficiency questions to take each statement individually first, and then look at them together if needed.

Sample Question:

Is the integer y a multiple of 4?

1) 3y2 is a multiple of 18.

2) y = p/q, where p is a multiple of 12 and q is a multiple of 3.

Solution:

Assessing Statement 1:

If 3y2 is a multiple of 18, we know that y2 must be a multiple of 6, because 18 divided by 3 equals 6.  If y2 is a multiple of 6 and y must be an integer, y2 could be 36, in which case y = 6, or it could be 144, in which case y = 12.  If y = 6. then y is not a multiple of 4 and the answer to our question … Read full post

GMAT Data Sufficiency: The Lazy Person’s Favorite Question Type?

June 16, 2011 by

By Guest Author Kurt Keefner

About 100 years ago there lived a man famous for pioneering a field he called “motion study.”  His name was Frank B. Gilbreth.  He specialized in making factories more efficient.  When Gilbreth first walked into a factory he was helping, what he did was to ask to meet the laziest worker there, because he figured that that person had already figured out how to be efficient.

We can all take a cue from Mr. Gilbreth when it comes to the GMAT.  A general principle is:  Do no more work than is necessary to get the answer. Nowhere does this principle apply more than on that unique question type known as Data Sufficiency.

Data Sufficiency is like a Zen puzzle:  the answer to the question is not the answer to the problem.  The answer to the problem is what combination of data statements would … Read full post

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