Articles published in Algebra

Two Minutes of GMAT Quant: A Breakdown (Part 3)

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Manhattan Prep GMAT Blog - Two Minutes of GMAT Quant a Breakdown Part 3Did 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.


Ready for the long awaited conclusion of how to tackle a quant problem in two minutes? We’ll finally get to the point where you can submit an answer! If you haven’t been keeping up, catch up here. Read more

Taking the new mini-GMAT for EMBA? Here’s how to prep! – Part 2

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Manhattan Prep GMAT Blog - Taking the New Mini-GMAT for EMBA Candidates? Here's How to Prep (Part 2) by Stacey KoprinceDid 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.


Last time, we talked about the IR and Verbal sections of the new Executive Assessment (EA) exam for EMBA candidates. Today, we’re going to dive into Quant and also talk more about your overall study. Read more

Think Like an Expert: How & When to Work Backwards on GMAT Problem Solving

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Manhattan Prep GMAT Blog - Working Backwards on GMAT Problem Solving by Ceilidh EricksonDid you know that you can attend the first session of any of our online or in-person GRE 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

Two Minutes of GMAT Quant: A Breakdown – Part 2

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Manhattan Prep GMAT Blog - Here's How to Use Your Two Minutes on GMAT Quant Part 2Did 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

Here’s How to do GMAT Unit Conversions Like a Pro

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blog-metricsSometimes 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

Manhattan Prep’s GMAT® study app is now available!

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


Download now!

iOS

Android


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How to Tackle Every Single GMAT Problem (Seriously!) – Part 2

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Last time, I introduced you to a set of principles that tie together everything we need to do on the GMAT.

Blog-Tackle-Pt2

If you haven’t already read that article, go ahead and do so now.

Here’s our framework again:

228 - Q Process 3

Today, we’re going to try this out on a Data Sufficiency problem.

Try this DS problem from the GMATPrep® free exams.
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When Your High School Algebra is Wrong: How the GMAT Breaks Systems of Equations Rules

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2-17-HighSchool-2If 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
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Memorize this and pick up 2 or 3 GMAT quant questions on the test!

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gmat-quant-tipsMemorize 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.

Screen Shot 2014-05-29 at 2.40.57 PM

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:

Screen Shot 2014-05-29 at 2.31.24 PM

Let’s see.

Screen Shot 2014-05-29 at 2.32.25 PM

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:

Screen Shot 2014-05-29 at 2.33.22 PM

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.

Screen Shot 2014-05-29 at 2.34.28 PM

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

The numerator: Screen Shot 2014-05-29 at 2.35.25 PM

The denominator: Screen Shot 2014-05-29 at 2.36.02 PM

They’re almost identical! Both of the Screen Shot 2014-05-29 at 2.37.06 PMterms cancel out, as do the Screen Shot 2014-05-29 at 2.37.41 PMterms, leaving me with:

Screen Shot 2014-05-29 at 2.38.29 PM

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:

Screen Shot 2014-05-29 at 2.39.05 PM

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

Screen Shot 2014-05-29 at 2.39.54 PM

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.

 

 

The 4 Math Strategies Everyone Must Master, Part 1

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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 four strategies.

* ” If mv < pv < 0, is v > 0?

“(1) m < p

“(2) m < 0”

All set?

How did you do the problem? Most quant questions have more than one possible approach and this one is no exception—but I want to use this problem to talk about a particular technique called Testing Cases.

This question is called a “theory” question: there are just variables, no real numbers, and the answer depends on some characteristic of a category of numbers, not a specific number or set of numbers. When we have these kinds of questions, we can use theory to solve—but that can get very confusing very quickly. Instead, try testing real numbers to “prove” the theory to yourself.

(Note: I chose a particularly tough question for this exercise; testing cases can also be useful and fast on easier questions!)

This problem gives one inequality:

“mv < pv < 0″

The test writers are hoping that you’ll say, “Oh, let’s just divide by v to get rid of it, so the equation is really m < p < 0.” But that’s a trap! Why?

When you divide an inequality by a negative, you have to flip the signs. But you don’t know whether v is positive or negative, so you don’t know whether to flip the signs! Never divide an inequality by a variable if you don’t know the sign of the variable.

The question itself contains a clue (two, actually!) pointing to this trap. The given inequality asks about “< 0” and the question also asks whether v > 0? Less than zero and greater than zero are code for “I’m testing you on positives and negatives.”
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