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:

A set of n identical triangles with angle x° and two sides of length 1 is assembled to make a parallelogram (if n is even) or a trapezoid (if n is odd), as shown. Is the perimeter of the parallelogram or trapezoid less than 10?

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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:

An isosceles triangle with one angle of 120° is inscribed in a circle of radius 2. This triangle is rotated 90° about the center of the circle. What is the total area covered by the triangle throughout this movement, from starting point to final resting point?

(A) 
(B) 
(C) 
(D) 
(E) 

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The Quant section of the GMAT is not a math test. Really, it isn’t! It just looks like one on the surface. In reality, they’re testing us on how we think.

As such, they write many math problems in a way that hides what’s really going on or even implies a solution method that is not the best solution method. Assume nothing and do not accept that what they give you is your best starting point!

In short, learn to reorient your view on math problems. When I look at a new problem, one of my first thoughts is, “What did they give me and how could it be made easier?” In particular, I look for things that I find annoying, as in, “Ugh, why did they give it to me in that form?” or “Ugh, I really don’t want to do that calculation.” My next question is how I can get rid of or get around that annoying part.

What do I mean? Here’s an example from the free set of questions that comes with the GMATPrep software. Try it!

* ” If ½ of the money in a certain trust fund was invested in stocks, ¼ in bonds, ¹/₅ in a mutual fund, and the remaining $10,000 in a government certificate, what was the total amount of the trust fund?

“(A) $100,000

“(B) $150,000

“(C) $200,000

“(D) $500,000

“(E) $2,000,000”

What did you get?

Here’s my thought process:

(1) Glance (before I start reading). It’s a PS word problem. The answers are round / whole numbers, and they’re mostly spread pretty far apart. I might be able to estimate to get the answer and I should at least be able to tell whether it’s closer to (A) or (E).

(2) Read and Jot. As I read, I jot down numbers (and label them!):

S = ¹/₂

B = ¹/₄

F = ¹/₅

C = 10,000

(3) Reflect and Organize. Let’s see. The four things should add up to the total amount. Three of those are fractions. Oh, I see—if I had four fractions, they should all add up to 1. So if I take those three and add them, and then subtract that from 1, that’ll give me the fractional amount for the C. Since I know the real value for C, I can then figure out the total.

But, ugh, adding fractions is annoying! You need common denominators. I’m capable of doing this, of course, but I really don’t want to! Isn’t there an easier way?

In this case, yes! Adding decimals or percents is really easy. Adding fractions is annoying. Plus, check it out, the fractions given are all common ones that we (should) have memorized. So change those fractions to percents (or decimals)!

(4) Work. Let’s do it!

S = ¹/₂  = 50%

B = ¹/₄ = 25%

F = ¹/₅ = 20%

C = 10,000

Wow, this is a lot easier. I know that 50 + 25 + 25 would equal 100, but I’ve only got 50 + 25 + 20, so the total is 5 short of 100. The final value, C, then must be 5% of the total.

So let’s see… if C = 10,000 = 5%, then 10% would be twice as much, or 20,000. And I just need to add a zero to get to 100%, or 200,000. Done! Read more

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:

A sheet of paper ABDE is a 12-by-18-inch rectangle, as shown in Figure 1. The sheet is then folded along the segment CF so that points A and D coincide after the paper is folded, as shown in Figure 2 (The shaded area represents a portion of the back side of the paper, not visible in Figure 1). What is the area, in square inches, of the shaded triangle shown?

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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 a, c, d, x, and y are positive integers such that ay < x and  is the lowest-terms representation of the fraction , then c is how much greater than d? (If  is an integer, let d = 1.)

(1)  is an odd integer.

(2) a = 4

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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:

The positive number a is q percent greater than the positive number b, which is p percent less than a itself.  If a is increased by p percent, and the result is then decreased by q percent to produce a positive number c, which of the following could be true?

I.    c > a
II.   c = a
III.  c < a

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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 a and b are different nonzero integers, what is the value of b ?

(1) a^b = ab

(2) a^b – a^{b – 1} = 2

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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:

A semicircular piece of paper has center O, as shown above. Its diameter A’A is coated with adhesive. If the adhesive is used to fuse radii OA’ and OA along their entire lengths (so that points A and A’ coincide, points P and P’ coincide, and so on), a cone is formed as shown above. If point B divides the original semicircle into two identical arcs, what is the measure of angle AOB in the folded cone?

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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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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 three different integers are selected at random from the integers 1 through 8, what is the probability that the three selected integers can be the side lengths of a triangle?

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