I'm toward the end of my second full month of tutoring in NYC, and it's been interesting to see how my GMAT students here differ from the gang that I taught in DC. I had an amazing range of students in DC, including a couple of people who started at or above 700, quite a few others who started in the high 300s or low 400s, and pretty much everything in between. My first group of NYC GMAT students, on the other hand, consists almost entirely of ass-kickers, gunning for something close to a 700. I've met two guys who have gone through every official GMAT question twice; both of them diligently kept notebooks of all of their mistakes, and still didn't get the scores they wanted. Pretty much everybody else I've met has graduated from a Kaplan, Veritas, Princeton Review, or Manhattan course. With only one exception, all of my students have consistently scored in the 600s on the real GMAT, and in the 600s and 700s on practice test.
So all of these guys know the GMAT really, really well. Generally, they start by asking questions about the tough stuff--combinatorics, hard rate problems, set theory, conditional probability, and the most vicious of sentence correction problems. Hardly any of these guys are the least bit worried about their algebra or arithmetic skills when they call me.
I have a few little files of "easy" GMAT questions, mostly consisting of basic algebra, arithmetic, and geometry. Eighth-grade level math, at most. Over the past few weeks, I've given the set to most of these veteran GMAT warriors.
How did they do? Well, one GMAT student got a perfect score, which is exactly what he should have done if he wants to get a 700. (I'm very proud of you, Mr. V. May the GMAT gods grant you a 750 and admission to the MBA program of your dreams.) Everybody else got ripped to shreds, missing somewhere between 15% and 30% of the questions. That would be fine on medium-to-hard (say, 600- or 700-level) GMAT questions, but nobody with dreams of admits from Harvard or Stanford should miss this kind of stuff.
Here are a few examples of reasonably easy questions that caused problems:
1. You drop a ball from a height of 16 meters. Each time you drop the ball, it bounces to a level half as high as its starting point. If you catch the ball after the fourth bounce, how far did the ball travel? (A) 30 meters (B) 31 meters (C) 40 meters (D) 41 meters (E) 45 meters
2. If x and y are two-digit integers such that x < 40, which of the following is closest to the maximum possible value of xy ? (A) 400 (B) 1,600 (C) 4,000 (D) 16,000 (E) 40,000
3. If the numbers 13/24, 9/16, 1/2, 2/3, and 5/8 were ordered from greatest to least, the middle number of the resulting sequence would be (A) 13/24 (B) 9/16 (C) 1/2 (D) 2/3 (E) 5/8
I'm not sure that any of these questions are much more than 500-level questions, but some good GMAT math students screw these up regularly, just because they don't read carefully, or because they rush through their calculations. Sometimes it seems that arithmetic and algebra questions cause 600+ scorers to immediately think "this is easy, I'm going to destroy this question in 25 seconds so I can move on to harder stuff"... and then they make a dumb mistake. I call this phenomenon "getting GMAT-ed."
The GMAT writes questions specifically to test your precision, and they're trying to get you to fall into traps by being imprecise or careless. If you don't count the bounces carefully, you won't get (E) for question 1. If you jump to conclusions on #2 (i.e. by misreading an inequality sign or by missing the word "two-digit"), you might not know that the answer is (C). There's nothing magical about question #3, but it's easy to get overconfident and make a calculation or comparison error. The answer, incidentally, is (B). Easily 30% of my 600+ students have missed a version of that last one, even though it's just a simple numerical comparison.
The moral of the story? If you read a GMAT math question and you think that it's easy, watch your back. Don't let overconfidence get in the way of your GMAT score. Check your answer twice--it's always worth spending an extra 15 seconds to make sure that you haven't done something silly that can damage your GMAT score.