Common GRE Math Mistakes by: Christopher Lele on March 27, 2012 | 3,344 Views March 27, 2012 Copy Link Share on Facebook Share on Twitter Email Share on LinkedIn Share on WhatsApp Share on Reddit General Mistake #1: Not reading the problem carefully Under timed conditions, you may feel compelled to rush. But remember, by misreading a word (or not reading it entirely), you can make a relatively straightforward problem seem intractable. You may flail about the answer choices, picking one ā usually the incorrect one ā that happens to be somewhat close to your answer. Worse yet, you may get a numeric entry question and blithely enter in the wrong answer, something you could easily have avoided doing had you read the question carefully. General Mistake #2: Flubbing the Math Many math mistakes result from forgetting something so minor as write a negative sign. Other times, simple mathematical errors, like thinking that 16 x 5 = 90 can be very costly. Math is about precision so use your prep time to become an efficient and unerring human calculator. Specific Mistakes Below are two common mistakes and oversights, along with problems that test those mistakes. See if you can avoid these common GRE mistakes. 1.Ā Ā Ā Ā Prime Numbers 2 is the smallest prime number. It is the only even prime. 1 is NOT a prime. 2.Ā Ā Ā Ā Donāt Forget 0 and 1 Especially in Quantitative Comparison, you always want to make sure to plug in 0 and 1 if the constraints permit doing so. Oftentimes plugging in a 0 or 1 will prove the exception, thus making the answer (D): āThe relationship cannot be determined from the information givenā. 3.Ā Ā Ā Ā Must Be vs. Could Be There is a subtle, but important difference here. If a question is phrasedĀ āmust beā, then the answer you choose must always hold true for the conditions stated in the problem. āCould beā means that in certain instances, i.e. for certain numbers. All of this makes a lot more sense when in the context of the problem. So letās take a look at a practice question. 1. c and d are prime numbers. IfĀ c – dĀ is an odd prime, then which of the following must be true? (A)Ā Ā cĀ is even (B)Ā Ā dĀ is odd (C)Ā Ā c x dĀ is odd (D)Ā dĀ is even (E)Ā Ā c x d ā c is even Explanation First off, donāt let the variables throw you. There is an answer, so there must be some pattern that you have to discern. If you remember, I mentioned that ā2ā is the only even prime. Thus the rest are all odds. The question says thatĀ c – dĀ is an odd prime. The only way to get an odd number when we subtract two numbers is that one number must be odd and one must be even. Since ā2ā is the only even prime we know that ā2ā must be d. (c cannot equal ā2ā becauseĀ c – dĀ would end up being negative number, and primes canāt be negative). We donāt have to know what exact number c equals. As long asĀ c – dĀ equals an odd prime.Ā c = 5Ā is perfect. We plug in those values into the question. Only D works. And we know that d must be even, because d must equal 2, an even number. Takeaway Keep both the general and specific mistakes in mind when you take the actual GRE, but also as youāre doing practice questions as you study– build good habits now so you donāt lose easy points on the day of the exam! This was written by Chris Lele, GRE Expert at Magoosh GRE Prep, and originally posted here.Ā DONāT MISS:Ā PREPPING FOR THE GREāS TEST OF YOUR READING COMPREHENSIONĀ orĀ PREPPING FOR THE GRE TEST OF YOUR QUANT LOGIC