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GMAT Club

Monday Mail-Bag: Advice on Big Picture Issues That Impact GMAT Test Takers…

EMPOWERgmat 0

by Rich Cohen,  Rich.C@empowergmat.com  www.EMPOWERgmat.com

This series of emails and PMs focuses on situations that many Test Takers face during their studies. The names of the original posters have been changed to protect their identities.

Number Properties in DS Questions
Hi Rich,

I’m stuck on this DS. What’s the easiest way to solve it?

If x and y are prime numbers, is y(x-3) odd ?

1) x > 10

2) y < 3 Xena Hi Xena, This DS question is built on Number Properties. We're told that X and Y are PRIME numbers. We're asked if "Y(X-3) is odd?" This is a YES/NO question. Here are the Number Properties worth knowing for this question: Odd x Odd = Odd Even x Odd = Even Even x Even = Even Fact 1: X > 10

Since X is PRIME and X > 10, this means that X MUST be ODD. By extension, since X is ODD, then this means that (X-3) MUST be EVEN (since odd – odd = even). Next, remember that ANY integer multiplied by an EVEN yields an EVEN? So Y(X-3) will ALWAYS be EVEN (by extension, it will NEVER be ODD), so the answer to the question is ALWAYS NO.
Fact 1 is SUFFICIENT

Fact 2: Y < 3

Since Y is PRIME, it MUST be 2. Here, we're dealing with the SAME Number Property rule as in Fact 1: Since Y is 2, 2(X-3) MUST be EVEN, so it will NEVER be odd – and the answer to the question is ALWAYS NO.
Fact 2 is SUFFICIENT

Final Answer: D

General Verbal Advice To Build Your Skills
Dear Rich,

I’m about to start studying for verbal, are there any general tips or advice that you can offer?

Yasmine

Hi Yasmine,

Before you begin your studies in the 3 major Verbal categories (SC, RC and CR), here are some ideas that you should start off with:

1) SCs usually represent the largest number of Verbal questions in that section of the GMAT, so you have to make sure you know the major GMAT grammar rules that are tested (and that knowledge will be worth a LOT of points). Some of this comes down to repetitions and memorization, the rest comes down to building a "library" of the patterns that the GMAT uses to test these various rules, so that you can spot the correct answers faster.

2) RC and CR prompts require notes. DO NOT try to answer these questions in your head. DO NOT run to the answers and pick the one that "sounds best." Learning to predict the correct answer before you look at the options will help you to speed up and increase your score.

TEST THE ANSWERS with Algebra
Rich,

Can we use the answers against this question? And if yes then how?

Each digit in the two-digit number G is halved to form a new two-digit number H. Which of the following could be the sum of G and H?

A. 153
B. 150
C. 137
D. 129
E. 89

The first sentence in this question provides an important piece of information. Since EACH of the digits is HALVED to form a new number, then each of those original digits MUST be EVEN.

Eg. 46 halved is 23, but 57 cannot be halved to form a new integer.

You can TEST THE ANSWERS on this question. Here's how….

The question mentions that G is "halved" to form H. In algebra terms, this means…

G/2 = H

When the question asks for what COULD be the sum of G and H, what it's REALLY asking is…

G + H = ?
G + G/2 = ?
3G/2 = 1.5G = ?

Which of these could be the value 1.5G (given the constraints of the question)?

Let's TEST answer E…

1.5G = 89

Now multiply both sides by 2 to get rid of the decimal…

3G = 178

178 is NOT evenly divisible by 3, so it CAN'T be the answer.

Let's TEST answer D…

1.5G = 129
3G = 258

G = 86; this IS a 2-digit number with EVEN digits!!!!

G=86, H=43, G+H = 129
This matches everything we were told in the prompt.

Final Answer: D

GMAT assassins aren't born, they're made,
Rich