### GMAT Challenge Problem Showdown: September 30, 2013

We invite you to test your GMAT knowledge for a chance to win! Each week, we will post a new Challenge Problem for you to attempt. If you submit the correct answer, you will be entered into that week’s drawing for a free Manhattan GMAT Prep item. Tell your friends to get out their scrap paper and start solving!

Here is this week’s problem:

For how many different pairs of positive integers (

a,b) can the fraction be written as the sum ?

### How To Solve Any Sentence Correction Problem, Part 2

In the first half of this article, we talked about the 5-step process to answer SC problems:

1. Take a *First Glance*

2. *Read* the Sentence

3. Find a *Starting Point*

4. *Eliminate* Answers

5. Repeat steps 3 and 4

If you haven’t already learned that process, read the first half before continuing with this part.

### Drills to Build Skills

How do you learn to do all of this stuff? You’re going to build some skills that will help at each stage of the way. You might already feel comfortable with one or multiple of these skills, so feel free to choose the drills that match your specific needs.

### Drill Number 1: First Glance

Open up your Official Guide and find some lower-numbered SC questions that you’ve already tried in the past. Give yourself a few seconds (no more than 5!) to glance at a problem, then look away and say out loud what you noticed in those few seconds.

As you develop your First Glance skills, you can start to read a *couple* of words: the one right before the underline and the first word of the underline. Do those give you any clues about what might be tested in the problem? For instance, consider this sentence:

Xxx xxxxxx xxxx xx and she xxx xxxxx xxxx xxxx xxx xxx xxxxx.

I can’t know for sure, but I have a strong suspicion that this problem might test parallelism, because the word *and* falls immediately before the underline. When I read the sentence, I’ll be looking for an *X and Y* parallelism structure.

At first, you’ll often say something like, “I saw that the underline starts with the word *psychologists* but I have no idea what that might mean.” (Note: this example is taken from OG13 SC #1!) That’s okay; you’re about to learn. Go try the problem (practicing the rest of the SC process as described in the first half of this article) and ask yourself again afterwards, “So what might I have picked up from that starting clue?”

The word *psychologists* is followed by a comma… so perhaps something will be going on with modifiers? Or maybe this is a list? The underline is really long as well, which tends to go with modifiers. Now, when you start to read the sentence, you will already be prepared to figure out what’s going on with this word. (In this case, it turns out that *psychologists* is followed only by modifiers; the original sentence is missing a verb!)

### Drill Number 2: Read the Sentence

Take a look at some OG problems you’ve tried before. Read only the original sentence. Then, look away from the book and articulate aloud, in your own words, what you think the sentence is trying to convey. You don’t need to limit yourself to one sentence. You can also glance back at the problem to confirm details.

I want to stress the “out loud” part; you will be able to hear whether the explanation is sufficient. If so, try another problem.

If you’re struggling or unsure, then one of two things is happening. Either you just don’t understand, or the sentence actually doesn’t have a clear meaning and that’s why it’s wrong! Decide which you think it is and then look at the explanation. Does the explanation’s description of the sentence match what you thought—the sentence actually does have a meaning problem? If not, then how does the explanation explain the sentence? That will help you learn how to “read it right” the next time. (If you don’t like the OG explanation, try looking in our GMAT Navigator program.)

### Drill Number 3: Find a Starting Point

Once again, open up your OG and look at some problems you have done before. This time, do NOT read the original sentence. Instead, cover it up. Read more

### Free GMAT Events This Week: September 30 – October 6

Here are the free GMAT events we’re holding this week. All times are local unless otherwise specified.

**9/30/13**– Chicago, IL – Free Trial Class- 6:30PM- 9:30PM

**10/1/13**– Princeton, NJ-Free Trial Class- 6:30PM- 9:30PM

**10/313**– Austin, TX- Free Trial Class– 6:30PM- 9:30PM

**10/5/13**– Online – Free Trial Class- 2:00PM- 5:00PM (EDT)

**10/5/13**– Online –Live Online GMAT Preview– 2:00PM- 3:30PM (EDT)

**10/5/13**– Arlington, VA- Free Trial Class- 10:00AM- 1:00PM

**10/6/13**– Durham, NC- Free Trial Class– 5:30PM- 8:30PM

**10/6/13**– Washington, DC – Essay Writing Workshop presented by mbaMission- 9:00PM- 12:00AM (EDT)

**10/6/13**– Chicago, IL-Free Trial Class – 10:00AM- 1:00PM

Looking for more free events? Check out our Free Events Listings Page.

### Be the Tiger Woods of Testing: Expert Performance and Deliberate Practice

*Consistently and overwhelmingly, the evidence showed that experts are always made, not born.* (“The Making of an Expert” by K. Anders Ericsson, Michael J. Prietula, and Edward T. Cokely, Harvard Business Review, July-August 2007)

Standardized test-taking is a *skill*–like winning a chess game, swinging a golf club, or playing a Bach concerto. And to master a skill, you need high-quality *practice*. Of course, the more content you know the better, but no matter how much you study for the GMAT, you won’t improve without practice. (I tried reading a book about snowboarding before my first time on the slopes, with predictably laughable results.) According to the scientific research, the most efficient and most effective kind of practice-the way Tiger Woods become the golfer he is today–is called “Deliberate Practice.”

If you spend time reading motivational blogs such as LifeHacker you’ll see many articles about “Deliberate Practice.” You may have even heard of whole books–Talent is Overrated by Geoffrey Colvin or Outliers by Malcolm Gladwell–about exceptional individuals such as Bobby Fischer and Tiger Woods. All those blogs, as well as Colvin and Gladwell, base their ideas on the research of K. Anders Ericsson, a Professor of Psychology at Florida State University and probably the world’s number-one expert on expertise. His good-news thesis can be summed up as follows:

New research shows that outstanding performance is the product of years of deliberate practice and coaching, not of any innate talent or skill.(Ericsson et al., “The Making of an Expert”)

First of all, relax. You may have heard about Ericsson’s 10,000 hour rule. Apparently, it takes about 10 years and 10,000 hours of “deliberate practice” to achieve true mastery. Yes, Tiger Woods, Bobby Fischer, Mozart, and other one-in-a-million people needed 10,000 hours to get to where they are. Luckily, the GMAT is much less difficult to master than golf, chess, or composition. Also, you’re not looking to be one in a million–at best 1 in 100 (a score of 760-800)–so you don’t need 10,000 hours. Maybe a few hundred hours, depending on how much you want to improve.

But what is “Deliberate Practice?” And how do you apply it to the GMAT? At the end of this article, I’ve given you a few links, but to save you time, I’ve pulled my favorite Ericsson quotes and applied them to the GMAT:

**1) Get motivated.**

The most cited condition concerns the subjects’ motivation to attend to the task and exert effort to improve their performance.(“The Role of Deliberate Practice in the Acquisition of Expert Performance” by K. Anders Ericsson, Ralf Th. Krampe, and Clemens Tesch-Romer. Psychological Review. 1993, Vol. 100. No. 3)

Moving outside your traditional comfort zone of achievement requires substantial motivation and sacrifice, but it’s a necessary discipline.(Ericsson et al., “The Making of an Expert”)

If you’re reading this, you want a higher GMAT score. You’re already motivated. If you need more motivation, research schools. Take a diagnostic test and see how far you are from your dream school’s median. After that, the best way to get motivated is to sign up for the real GMAT a few months from now. (How many people don’t lose weight until they schedule the wedding or high school reunion?) Read more

### Story Problems: Make Them Real (Part 2)

Last time, we talked about how to make story problems real; if you haven’t read that article yet, go take a look before you continue with this one.

I’ve got another one for you that’s in that same vein: the math topic is different, but the “story” idea still hold in general. This one has something extra though: you need to know how a certain math topic (standard deviation) works in general. Otherwise, you won’t be able to think your way through the problem.

Try this GMATPrep® problem:

* ” During an experiment, some water was removed from each of 6 water tanks. If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?

“(1) For each tank, 30 percent of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.

“(2) The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.”

Standard deviation! Ugh. : )

Okay, it’s no accident that they’re using a DS-format problem for this one. It’s not possible to calculate a standard deviation in 2 minutes without a calculator (unless, perhaps, that standard deviation is zero!). They never expect us to calculate standard deviation on this test, but they do want to know whether we understand the concept in general.

So what is standard deviation? Try to answer—aloud—in your own words before you continue reading.

(Why did I say “aloud”? Often, we tell ourselves that we *can* explain something, but not until we actually try do we realize that we need a refresher on the concept. Giving an explanation aloud forces you to prove that you really do know how to explain the concept. If you don’t, you’ll hear your uncertainty in your own explanation.)

Standard deviation is the measure of how spread apart a set of data points is. For example, let’s say you have the following 5 numbers in a set: {3, 3, 3, 3, 3}. The standard deviation is zero because the numbers are all exactly the same—there is no “spread” at all in the set.

Which of the following two sets has a larger standard deviation?

{1, 2, 3, 4, 5}

{1, 10, 20, 80, 2,000}

The second one! The numbers are much more spread apart than in the first set.

Right now, some of you are wondering: okay, but what’s the actual standard deviation of those two sets?

I don’t know. I could calculate it—I’m sure there are many online “standard deviation” calculators I could use. But I don’t care. The real test is never going to make me calculate this! (And that’s why I haven’t gotten into the actual calculation method here… nor will I.)

There are a few concepts that we should know, though, in terms of how changes to sets can affect the standard deviation. Read more

### Free GMAT Events This Week: September 23 – September 29

Here are the free GMAT events we’re holding this week. All times are local unless otherwise specified.

**9/23/13**– Bellaire, TX – Free Trial Class- 6:30PM- 9:30PM

**9/23/13**– Denver, CO- Free Trial Class– 6:30PM- 9:30PM

**9/2413**– Online- MBA Admissions Myths Destroyed presented by mbaMission– 4:00PM- 5:30PM (EDT)

**9/24/13**– London – Free Trial Class- 6:30PM- 9:30PM

**9/24/13**– San Antonio, TX – Free Trial Class- 6:30PM- 9:30PM

**9/24/13**– Washington, DC- Free Trial Class– 6:30PM- 9:30PM

**9/25/13**– Santa Monica, CA- Free Trial Class- 6:30PM- 9:30PM

Read more

### Manhattan GMAT Launches New Palo Alto And Upper East Side Classes

Exciting news for GMAT preppers on both coasts! Today we’re announcing two new Manhattan GMAT class locations that will make taking a Manhattan GMAT course even more convenient.

Starting October 9th, we will offer GMAT classes in Palo Alto, California. Our new Palo Alto location joins our other San Francisco Bay Area locations in San Francisco, Berkeley, and Santa Clara. Details on our Palo Alto Fall A course can be found here.

We’re also pleased to announce a new Upper East Side class to join our West 25th Street flagship and Wall Street location in New York City. The UES location is conveniently located near the 6 train on the east side of Manhattan at 221 East 71st Street. Details about NYC [Upper East Side] Fall A, which also starts on October 9th, can be found here.

Both locations will be staffed by our famous 99th percentile instructors. You can read more about what makes them so special here. Not in the San Francisco Bay Area or New York City? You can look at all our upcoming classes here.

### Story Problems: Make Them Real

I’ve been on a story problem kick lately. People have a love / hate relationship with these. On the one hand, it’s a story! It should be easier than “pure” math! We should be able to figure it out!

On the other hand, we have to figure out what they’re talking about, and then we have to translate the words into math, and then we have to come up with an approach. That’s where story problems start to go off the rails.

You know what I mean, right? Those ones where you think it’ll be fine, and then you’re about 2 minutes in and you realize that everything you’ve written down so far doesn’t make sense, but you’re sure that you can set it up, so you try again, and you get an answer but it’s not in the answer choices, and now you’re at 3.5 minutes or so… argh!

So let’s talk about how to make story problems REAL. They’re no longer going to be abstract math problems. You’re riding Train X as it approaches Train Y. You’re the store manager figuring out how many hours to give Sue so that she’ll still make the same amount of money now that her hourly wage has gone up.

Try this GMATPrep® problem:

* ” Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

“(A) 2

“(B) 3

“(C) 4

“(D) 6

“(E) 8”

Yuck. A work problem.

Except… here’s the cool thing. The vast majority of rate and work problems have awesome shortcuts. This is so true that, nowadays, if I look at a rate or work problem and the only solution idea I have is that old, annoying RTD (or RTW) chart… I’m probably going to skip the problem entirely. It’s not worth my time or mental energy.

This problem is no exception—in fact, this one is an amazing example of a complicated problem with a 20-second solution. Seriously—20 seconds!

You own a factory now (lucky you!). Your factory has 6 machines in it. At the beginning of the first day, you turn on all 6 machines and they start pumping out their widgets. After 12 continuous days of this, the machines have produced all of the widgets you need, so you turn them off again.

Let’s say that, on day 1, you turned them all on, but then you turned them off at the end of that day. What proportion of the job did your machines finish that day? They did 1/12 of the job.

Now, here’s a key turning point. Most people will then try to figure out how much work one machine does on one day. (Many people will even make the mistake of thinking that one machine does 1/12 of the job in one day.) But don’t go in that direction in the first place! If you were really the factory owner, you wouldn’t start writing equations at this point. You’d figure out what you need by testing some scenarios. Read more

### GMAT Challenge Problem Showdown: September 16, 2013

We invite you to test your GMAT knowledge for a chance to win! Each week, we will post a new Challenge Problem for you to attempt. If you submit the correct answer, you will be entered into that week’s drawing for a free Manhattan GMAT Prep item. Tell your friends to get out their scrap paper and start solving!

Here is this week’s problem:

If

aandbare different nonzero integers, what is the value ofb?(1)

a=^{b}ab(2)

a–^{b}a^{b}^{ – 1}= 2

### Free GMAT Events This Week: September 16 – September 22

Here are the free GMAT events we’re holding this week. All times are local unless otherwise specified.

**9/16/13**– Boston, MA – Free Trial Class- 6:30PM- 9:30PM

**9/16/13**– Dallas, TX- Free Trial Class– 6:30PM- 9:30PM

**9/1613**– Online- Choosing the Right B-School presented by mbaMission– 12:00PM- 1:30PM (EDT)

**9/16/13**– Minneapolis, MN – Free Trial Class– 6:30PM- 9:30PM

**9/16/13**– Atlanta, GA – Free Trial Class– 6:30PM- 9:30PM

**9/17/13**– Madison, WI- Free Trial Class– 6:15PM- 9:15PM

**9/17/13**– Online- Free Trial Class- 8:00PM- 11:00PM (EDT)

**9/17/13**– Toronto, ON – Free Trial Class- 6:30PM- 9:30PM

**9/18/13**– Online- Live Online GMAT Preview– 8:00PM- 9:30PM

**9/19/13**– Online- Free Trial Class– 8:00PM- 9:30PM (EDT)

**9/21/13**– Austin, TX- Free Trial Class- 1:00PM- 4:00PM

**9/22/13**– Boston, MA – Free Trial Class– 5:30PM- 8:30PM

**9/22/13**– Irvine, CA – Free Trial Class– 5:30PM- 8:30PM

**9/22/13**– Online- Free Trial Class- 2:00PM- 5:00PM (EDT)

Looking for more free events? Check out our Free Events Listings Page.