Did you know that you can attend the first session of any of our online or in-person GMAT courses absolutely free? We’re not kidding! Check out our upcoming courses here.

What does it take to be a GMAT expert? It’s not just content knowledge (although of course that’s necessary). A GMAT expert knows how to quickly identify patterns and choose quickly from a variety of strategies. In each of these segments, I’ll show you one of these expert moves and how to use it. Read more

Did you know that you can attend the first session of any of our online or in-person GMAT courses absolutely free? We’re not kidding! Check out our upcoming courses here.

If you read the first post in this series, then you already know how to get the most you can out of the first 5 seconds of a GMAT Quant problem. But what about the other 1:55? Let’s continue to delve. Read more

Sometimes the whole point of a specific GMAT problem is to convert between miles and kilometers, or meters and centimeters. In other problems, you’ll need to do a unit conversion as part of a longer solution. It’s easy to mess up unit conversions, and the GMAT writers know this — they include them on the test in order to test your level of organization and your ability to double-check your work. Here’s how to add fast unit conversions to your repertoire of skills.   Read more

I am very excited to announce that our new GMAT® study app is available on both iOS and Android!

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If you have two equations, you can solve for two variables.

This rule is a cornerstone of algebra. It’s how we solve for values when we’re given a relationship between two unknowns:

If I can buy 2 kumquats and 3 rutabagas for $16, and 3 kumquats and 1 rutabaga for $9, how much does 1 kumquat cost?

We set up two equations:

2k + 4r = 16

3k + r = 9

Then we can use either substitution or elimination to solve. (Try it out yourself; answer* below).

On the GMAT, you’ll be using the “2 equations à 2 variables” rule to solve for a lot of word problems like the one above, especially in Problem Solving. Be careful, though! On the GMAT this rule doesn’t always apply, especially in Data Sufficiency. Here are some sneaky exceptions to the rule…

2 Equations aren’t always 2 equations
Read more

Memorize what? I’m not going to tell you yet. Try this problem from the GMATPrep® free practice tests first and see whether you can spot the most efficient solution.

All right, have you got an answer? How satisfied are you with your solution? If you did get an answer but you don’t feel as though you found an elegant solution, take some time to review the problem yourself before you keep reading.

Step 1: Glance Read Jot

Take a quick glance; what have you got? PS. A given equation, xy = 1. A seriously ugly-looking equation. Some fairly “nice” numbers in the answers. Hmm, maybe you should work backwards from the answers?

Jot the given info on the scrap paper.

Step 2: Reflect Organize

Oh, wait. Working backwards isn’t going to work—the answers don’t stand for just a simple variable.

Okay, what’s plan B? Does anything else jump out from the question stem?

Hey, those ugly exponents…there is one way in which they’re kind of nice. They’re both one of the three common special products. In general, when you see a special product, try rewriting the problem usually the other form of the special product.

Step 3: Work

Here’s the original expression again:

Let’s see.

Interesting. I like that for two reasons. First of all, a couple of those terms incorporate xy and the question stem told me that xy = 1, so maybe I’m heading in the right direction. Here’s what I’ve got now:

And that takes me to the second reason I like this: the two sets of exponents look awfully similar now, and they gave me a fraction to start. In general, we’re supposed to try to simplify fractions, and we do that by dividing stuff out.

How else can I write this to try to divide the similar stuff out? Wait, I’ve got it:

The numerator: 

The denominator: 

They’re almost identical! Both of the terms cancel out, as do the terms, leaving me with:

I like that a lot better than the crazy thing they started me with. Okay, how do I deal with this last step?

First, be really careful. Fractions + negative exponents = messy. In order to get rid of the negative exponent, take the reciprocal of the base:

Next, dividing by 1/2 is the same as multiplying by 2:

That multiplies to 16, so the correct answer is (D).

Key Takeaways: Special Products

(1) Your math skills have to be solid. If you don’t know how to manipulate exponents or how to simplify fractions, you’re going to get this problem wrong. If you struggle to remember any of the rules, start building and drilling flash cards. If you know the rules but make careless mistakes as you work, start writing down every step and pausing to think about where you’re going before you go there. Don’t just run through everything without thinking!

(2) You need to memorize the special products and you also need to know when and how to use them. The test writers LOVE to use special products to create a seemingly impossible question with a very elegant solution. Whenever you spot any form of a special product, write the problem down using both the original form and the other form. If you’re not sure which one will lead to the answer, try the other form first, the one they didn’t give you; this is more likely to lead to the correct answer (though not always).

(3) You may not see your way to the end after just the first step. That’s okay. Look for clues that indicate that you may be on the right track, such as xy being part of the other form. If you take a few steps and come up with something totally crazy or ridiculously hard, go back to the beginning and try the other path. Often, though, you’ll find the problem simplifying itself as you get several steps in.

* GMATPrep® questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.

We need to know a lot of different facts, rules, formulas, and techniques for the Quant portion of the test, but there are 4 math strategies that can be used over and over again, across any type of math—algebra, geometry, word problems, and so on.

Do you know what they are?

Try this GMATPrep® problem and then we’ll talk about the first of the 4 math strategies.

*If mv < pv < 0, is v > 0?

(1) m < p

(2) m < 0

All set? Read more

On the GMAT, you may see a 3 to 5 ratio expressed in a variety of ways:

3:5
3 to 5
x/y = 3/5
5x = 3y (Yes, that’s the same as the other 3. Think about it.)

In the real world, we encounter ratios in drink recipes more often than anywhere else (3 parts vodka, 5 parts cranberry), perhaps explaining why–after drinks that strong–we forget how to handle them.

Keep in mind: ratios express a “part to part” relationship, whereas fractions and percentages express a “part to whole” relationship. So the fraction of the above drink is 3/8 vodka (or 37.5% of the whole). Either way, hold off on mixing that drink until after this post.

I like to set up ratios using a “ratio box.” The box is a variant on the “Unknown Multiplier” technique from page 65 of our FDPs book, but it’s a nice way to visually manage ratios without resorting to algebra.

Let’s take the beginning of a typical ratio question:

“The ratio of men to women in a class is 3:2…”

Instead of doing anything fancy with variables, I just set up a tracking chart:

From this point alone, I have sufficient information to answer a bunch of questions.

-What fraction of the students are men? (3/5)

-What percent of the students are women? (40%)

-What is the probability of choosing a man? (3/5)

-etc.

However, I have nowhere near enough information to answer anything about the REAL numbers of students in this class. Suppose the GMAT were to add a little more information:

“The ratio of men to women in a class is 3:2. If there are 35 students in the class…”

Now we can calculate almost everything about the real numbers of people. First, make a bigger box with 3 lines. The unfilled box looks like this:

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“Many a true word is said in jest.”—I don’t know, but I heard it from my mother.

Once upon a time in America, when I was a boy, my father, an engineer, said to me, “You can make numbers do anything you want them to do.”  This was the beginning of my cynicism.  But never mind that.  My father was fluent in four languages: English, German, French, and Algebra.  My father was also a very honest man.  His comment relied on the fact that most people can’t read Algebra—he just let people fool themselves.  Teaching GMAT classes, I combat the fact that many people can’t read Algebra.  Like my father, the GMAT exploits that weakness and lets—nay, encourages—people to fool themselves.  Thus, for many, preparing for the quantitative portion of the GMAT is akin to studying a foreign language.  (I know that even many native speakers feel that preparing for the verbal portion of the GMAT is also akin to studying a foreign language.  But that’s a different topic.)  In any case, you want to make your Algebra as fluent as your French. . .yes, for most of you, that was one of those jokes.

I know that some of you disagreed with the above and feel that the problem is an inability to understand math.  But that’s not true, at least on the level necessary to succeed on the GMAT.  If you really didn’t have enough synapses, they wouldn’t let you out without a keeper—because you couldn’t tip, or comparison shop, or count your change.  It’s a literacy problem.  Think about the math units in the course.  Truthfully, the first one is often a death march.  By the end, as country folk say, I often feel like I’m whipping dead horses.  On the other hand, the lesson concerning probability and combinations, putatively a more advanced topic, usually goes really well.  Why?  Because folks can read the words and understand their meaning.  Conversely, folks just stare at the algebraic symbols as if they were hieroglyphics.  The problem is that putting a Rosetta Stone in the book bag would make it weigh too much. . .kidding.  But if you can’t read the hieroglyphics, the mummy will get you—just like in the movies.

It really is a literacy issue and should be approached in that fashion.  You still don’t believe me?  You want specific examples?  I got examples, a pro and a con.  On the affirmative side, I once worked one on one with a man who came to me because his math was in shreds.  Because he couldn’t read what the symbols were saying.  Partly because his mother had once said, “Your sister is the one that’s good at math.”  As far as the GMAT is concerned, she was wrong, and so was your mother, if she said that.  Anyway, one day I gave him a high level Data Sufficiency word problem concerning average daily balances on a credit card.  He looked at it for about 30 seconds, and he didn’t write anything on his scrap paper.  Then he turned to me and said the answer was blah blah.  And he was right.  I looked at him and said, “How did you do that?  You’re not that good.”  (Yes, this is also an example of how mean I am to private students.)  But—and here’s the real punch line—he said, “It was about debt; I understood what the words meant.”  And there you go.  As a by the way, he worked very hard, became competent although not brilliant quantitatively, scored 710—97%V, 72%Q*—and went to Kellogg.

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This is the second of a series of posts that offer alternate ways to solve certain GMAT problems (check out the first here: DS Value Problems). Just like last time, if you like the method, steal it! And if you don’t, I promise not to lose any sleep. There’s a lot of ways to solve most questions on the GMAT and the best way will always be the way that works best for you. So without further ado, let’s check out a GMATPrep question and see how fast you can solve:

Last month 15 homes were sold in Town X. The average (arithmetic mean) sale price of the homes was $150,000 and the median sale price was $130,000. Which of the following statements must be true?

I. At least one of the homes was sold for more than $165,000.

II. At least one of the homes was sold for more than $130,000 and less than $150,000.

III. At least one of the homes was sold for less than $130,000.

 

(A) I only

(B) II only

(C) III only

(D) I and II

(E) I and III

First things first, if you answered this question using algebra, you’re in great company. Another one of our instructors, Stacey Koprince, has a great write up on the algebra in this question, and it’s definitely worth a read-through right here. But a lot of questions on the GMAT, including this one, can be solved by thinking of extremely simple scenarios, rather than the algebra that determines all of them.

The first thing I noticed on this question is that this is one of those awful questions where there’s a whole lot of wiggle room with the information that they give you. What was the cheapest house? What was the cost of the third most expensive house? Were any of the houses all the same price? If the second cheapest house is half as expensive as the most expensive, how does that affect the cost of the other houses? It’s easy to get lost when you start to think about how little you know in this scenario.

But before I jump around and start picking values out of thin air, the most important part of this problem are the (few) things that MUST be true. In this case, there are two: the 15 house prices have a mean of $150,000 and a median of $130,000. And on my paper, I would write out a few slots to represent the house prices like this: (note- I wouldn’t write out all 15 slots. Just the first few, the last few, and, since this is a median problem, one in the middle.)

Again, there are two things that they tell me here, but I want to start with the most restrictive element in this problem. There are lots of different ways to get a mean of $150,000, but in order to get a median of $130,000, I would need at least one house to cost EXACTLY $130,000. So I add that to my chart (ignoring the $ sign and extra zeroes):

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