How to Improve GMAT Quant from Q49 to a Perfect Q51 Updated on Aug 28th, 2020 Many people on the forum are not happy with their 79th percentile Q49 scores. These are good scores, but understandably some require a higher score to beat their competition. This guide is designed to be a comprehensive overview for serious test-takers (those who previously achieved Q49) who are looking to get to the elusive Q51. Important: You only have one shot at the Q51 on your test. You will face a handful of elite questions and you need to be ready to face them. Here is a detailed inventory of the tough Q51 question types, concepts, and tips on how to handle them. For an overview of what question types appear on the GMAT, see this post: https://gmatclub.com/forum/overview-of- ... 11809.html 1. Do I have to get ALL Quant questions right to Q51? Answer: You do not have to answer all questions correctly; however, you must reach the hard questions, which is accomplished by answering 15-20 questions correctly in succession. Since the GMAT Math exam is in CAT form (Computer Adaptive Test), the questions increase in difficulty as you correctly answer questions, and get easier when you answer easy questions incorrectly. Therefore, after answering the first 7 questions correctly, you can expect your score to be around 35-40. These first few questions will be fairly basic and straightforward. In fact, you will have to keep going for a while, as the questions that are representative of a score of 50-51 usually appear after question number 17. Therefore, it is crucial to get the first 17 questions right as otherwise, you will not be able to reach the challenging questions that provide the opportunity to attempt achieving Q50/51. 2. What Concepts/Topics Do I Focus on when Targetting Q51 Score? Overview: It is vital to note in preparation for GMAT Math that Integer Properties, Statistics, Probability, Inequality, and Absolute Value are the 5 most important topics (Key Topics) that account for 60% of the GMAT math questions, and 80-90% of 50-51 level questions. Among them, Integer Properties and Statistics are especially important. If you get every question right in the “Integer” section, your score can go up as high as the mid-40s, and if you get every question right in the “Integer and Statistics” sections, you can expect to achieve a score in the high 40s for the Math section. Thus, it is vital that you correctly answer every key question from these five topics to score a 51. Integer Properties and Statistics . One question format in particular that keeps reoccurring is a question with a combination of 2 or 3 concepts of “different positive integers, median, mean, range, absolute value, and inequality” (that is what we have seen on the test and what we continually hear from our students). Answering it correctly or incorrectly will be the deciding factor in whether you get the perfect score or not – no second chances. These can be both PS or DS questions, and they are especially challenging in the DS section, as they are designed to look deceivingly obvious or simple, for example, questions dealing with 3 variables but only 2 equations/data points. (Note: Math Revolution has a methodology that provides you the knowledge required to answer up to 80% of easy/medium DS questions without solving them by matching the number of variables and the number of equations). It is not easy to solve these types of questions in just two minutes and they are purposely designed this way. Here are 2 examples of the Statistics and Integer Questions: Statistics: There are 3 different positive integers. If their average (the arithmetic mean) is 8, what are their values? 1) The largest integer is twice the smallest integer. 2) One of them is 9. →The correct answer is A . Integer Properties: The smallest of 7 positive integers is 1. Is the range of them greater than 3? 1) The average (the arithmetic mean) of them is 4. 2) The median of them is 4. → The correct answer is A . Logic Questions – On the path to Q51, you must master answering Trick Questions or, as we call them, “Common Mistake Type” questions. If you answer these questions incorrectly, the highest you can achieve is Q49. Side Note: What is a “Common Mistake Type” Trap Question? There are 5 types of questions that GMAT Math test makers design to trap students. Here are 2 of the most commonly used on the DS: DS Common Mistake Type 4 (A): If answer choice C seems too attractive and obvious, go back and check choice A or B alone. Look at the example below. If m and n are integers, is mn even? (1) m = 5. (2) m and n are consecutive integers. → The correct answer is B . DS Common Mistake Type 4 (B) If answer choice A or B seems too attractive and obvious, consider answer choice D. Look at the example below. If a, b, c, and d are different positive odd numbers, what is the median of the numbers? (1) a + b + c + d = 16. (2) The product of 3 numbers of a, b, c, or d is 15. → The correct answer is D . TIP! Important to note that the GMAC likes to use DS questions as the deciding factor for their Q50/Q51 scores…. most likely because DS questions are unique to the GMAT and thus provide a good level “measuring stick” even for individuals with a strong quantitative background. Therefore, if you are looking to score Q51, you will need to pay especially careful attention to the DS questions and learn how to spot Common Mistake Type questions. 3. Analysis of Specific Question Types to Master for Q51 DS Tips: As mentioned above, Integer and Statistics are the main chapters to focus on DS. Besides the “Mistake Type”, one specific type of DS questions to master is Hidden Integer Questions. These questions often present prices of products, the number of fruit, coins, people, stamps, cars, etc as “hidden integers”. These are countable numbers that are not given to increase complexity. These are logic questions and you should solve them logically rather than calculation. It is possible to calculate and solve these questions that way but it takes much longer and a lengthy calculation is exactly the trap the test wants to catch you with – to waste your time and slow you down. Integer Properties: M bought several pencils. If each pencil cost either 23-cent or 21-cent, how many 23-cent pencils did M buy? 1) M bought a total of 6 pencils 2) The total price of all pencils M bought was 130 cents → The answer choice C is very attractive, but the correct answer is B . Pencil is a hidden integer, but if you don’t recognize this fact, you would say C is the answer. In addition, Statement 1 is actually not giving you any helpful information Among Common Mistake Type questions, there are many cases in which A or B easily seems like a correct answer – when, in fact, D is the correct answer. One or two questions of this type play a decisive role in leading to a perfect 51. Integer Properties: Numbers a and b are positive integers. If a^4 - b^4 is divided by 3, what is the remainder? 1) When a + b is divided by 3, the remainder is 0. 2) When a 2 + b 2 is divided by 3, the remainder is 2. → The correct answer is D . In addition, You should be comfortable tackling inequality problems such as “greater than” and “less than” questions if you want to get a perfect 51. You should practice these so that your mind clicks when asked to figure out the minimum value (if asked “greater than”) and the maximum value (if asked “less than”). Statistics: There are five homes. If the median price of a home is $200,000, is the range of all prices greater than $80,000? 1) The average price of the five homes is $240,000. 2) Three of the five homes have the same price. → C looks like a right answer choice at first. However, the correct answer is A . Of course we would be incomplete if we did not include the famous DS Probability questions that you are likely to see on your quest to Q51. Here is an example: Probability: There are only apples and oranges in a box. What is the probability that the fruit selected at random from the box is an apple? 1) There are 2 apples in the box 2) The ratio of the number of apples to the number of oranges is 1 to 4. → C looks like a right answer choice, but the correct answer choice is B . In case of Absolute Value questions, a question regarding the relationship among |a|, a, and -a will determine a perfect 51. Absolute value: If |r|>|s|, is r>s? 1) r>0 2) s>0 → C is an attractive answer choice but A is a correct answer. Problem Solving Tips Be prepared to see questions about finding Hidden Integers and problems on the so-called “Pigeonhole Principle”. You have a good chance of seeing one of them. We have provided the definition of the Hidden Integer questions above in the DS section. Tip: if you see integer questions just like the number of fruits, people, animals, stamps, and candies, it is a good chance you are facing this question type. The name of Pigeonhole principle comes from the old problem of having to calculate the number of cases of pigeons entering pigeon lofts. (it will more clear once you read the example below). Integer Properties: There are 10 red balls, 10 blue balls, and 10 white balls in a box. What is the maximum number of balls you can draw from the box and have fewer than 5 balls of the same color drawn? A. 4 B. 5 C. 6 D. 10 E. 12 → This question asks for the maximum number of balls you can have, so the correct answer should be the unluckiest case. If you draw 4 red balls, 4 blue balls and 4 white balls all together, there can be no more than 4 balls of the same color. Hence, the correct answer choice is E . Questions related to Murphy’s Law and Sally’s Law are the questions for a perfect 51 in PS. * (Integer) There are 5 locks and 5 keys and each of the 5 keys matches each of the 5 locks. What is the minimum and the maximum trial numbers of attempts needed to confirm that each of the 5 keys matches each of the 5 locks? A. 5,15 B. 4,15 C. 5,10 D. 4,10 E. 5,20 → D is the correct answer choice. Can you figure out how to solve it quickly? Good – remember this approach so you can refer to it on your test. 5. Conclusion In this way, a perfect 51 is not an outcome of luck; you have to concentrate to excel in Integer and Statistics parts to that end. Especially, DS questions often will be the determining factor of a perfect Q51, and, therefore, you should not be misled by Mistake types. Please pay special attention to the Mistake type questions. Please remember solving 37 questions in 75 minutes in the actual GMAT exam is a big challenge. You will need to manage time effectively to solve hard questions in 2 minutes or less per question. How can you reduce the time spent per question significantly? Since GMAT is a logical test, you should not question whether you can solve a problem or not, but you should practice reaching answers logically without having to solve problems. *** We are math experts and if you find any grammatical issues – that is because we spend all of our time focusing on math; sorry grammar. Note that the information herein is based on the knowledge and experience of Max Lee, who taught 30,000+ students and solved 100,000+ problems in the past 15 years. He discovered and analyzed types of GMAT Math questions after continuous and numerous interviews with students who have achieved a score of 49 to 51 in the actual GMAT exam. Thus, please note that the information is herein is based solely on the experience of Max Lee. Due to the nature of the test and lack of transparency about the algorithm this guide is a best-effort attempt based on the best information available. If you have any questions or different information, please post it here for the benefit of the community.

=> Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. In remainder questions, you get the same answer if you do the divisions first and calculate with the remainders or do the calculations first and then find the remainder. Since 12 = 13*1 + (-1), 12 , the remainder when 12^{mn} is divided by 13 is the same as the remainder when (-1)^{mn} is divided by 13 . If mn is an odd number, (-1)^{mn} = -1 and if mn is an even number, (-1)^{mn} = 1 . The question asks if mn is an odd number or an even number. Condition 1) If m is an even integer, mn is an even number and the remainder when 12^{mn} is divided by 13 is 1 . Condition 1) is sufficient, since it yields a unique answer. Condition 2) If m = 2 and n = 1 , then 12^{2*1} = 12^2 = 144 = 13*11 + 1 and the remainder is 1 . If m = 1 and n = 1 , then 12^{1*1} = 12^1 = 12 = 13*0 + 12 and the remainder is 12 . Condition 2) is not sufficient since it does not yield a unique answer. Therefore, A is the answer. Answer: A

=> Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. Visit https://www.mathrevolution.com/gmat/lesson for details. Since we have 3 variables ( x, y and z ) and 0 equations, E is most likely the answer. So, we should consider conditions 1) & 2) together first. After comparing the number of variables and the number of equations, we can save time by considering conditions 1) & 2) together first. Conditions 1) & 2) We have x + y + z = 20 from condition 1) and 2x + 3y + 10z = 100 from condition 2). When we subtract two times the first equation from the second equation, we have y + 8z = (2x + 3y + 10z) - 2(x + y + z) = 100 – 2*20, 2x + 3y + 10z - 2x - 2y - 2z = 100 - 40, y + 8z = 60, and y = 60 - 8z. Then we notice that x = 9, y = 4, z = 7 and x = 2, y = 12, z = 6 are solutions of the equation system with x + y + z = 20 and 2x + 3y + 10z = 100. Since both conditions together do not yield a unique solution, they are not sufficient. Therefore, E is the answer. Answer: E In cases where 3 or more additional equations are required, such as for original conditions with “3 variables”, or “4 variables and 1 equation”, or “5 variables and 2 equations”, conditions 1) and 2) usually supply only one additional equation. Therefore, there is an 80% chance that E is the answer, a 15% chance that C is the answer, and a 5% chance that the answer is A, B or D. Since E (i.e. conditions 1) & 2) are NOT sufficient, when taken together) is most likely to be the answer, it is generally most efficient to begin by checking the sufficiency of conditions 1) and 2), when taken together. Obviously, there may be occasions on which the answer is A, B, C or D.

=> Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. We can determine whether a number is divisible by 4 from its final two digits. Numbers with the final digits 16, 36, 56, 76 and 96 are divisible by 4 and those with final digits 06, 26, 46, 66 and 88 are not divisible by 4 . Thus, asking whether n is divisible by 4 is equivalent to asking whether b is odd. Since it implies that both a and b are odd integers, condition 2) is sufficient. Condition 1) There are two cases to consider. If a is an even integer and b is an odd integer, the answer is ‘yes’. If a is an odd integer and b is an even integer, the answer is ‘no’. Since it does not yield a unique solution, condition 1) is not sufficient. Therefore, B is the answer. Answer: B

=> Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. We require infinitely many values to determine f(x) and g(x) . Since the original condition includes infinitely many variables and 0 equations, E is most likely to be the answer. So, we should consider conditions 1) & 2) together first. After comparing the number of variables and the number of equations, we can save time by considering conditions 1) & 2) together first. Conditions 1) & 2) f(g(2)) = f(2^2) = f(4) = 3*4 – 2 = 12 – 2 = 10 Therefore, C is the answer. Answer: C In cases where 3 or more additional equations are required, such as for original conditions with “3 variables”, or “4 variables and 1 equation”, or “5 variables and 2 equations”, conditions 1) and 2) usually supply only one additional equation. Therefore, there is an 80% chance that E is the answer, a 15% chance that C is the answer, and a 5% chance that the answer is A, B or D. Since E (i.e. conditions 1) & 2) are NOT sufficient, when taken together) is most likely to be the answer, it is generally most efficient to begin by checking the sufficiency of conditions 1) and 2), when taken together. Obviously, there may be occasions on which the answer is A, B, C or D.

=> Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. The formula a n =a n-2 +3 tells us that alternate terms have the same remainder when they are divided by 3. Since a 1 = 111 = 3*37 is a multiple of three, all multiples of three greater than 111 can be obtained as odd-numbered terms. Therefore, 411= 3*137 is one of the odd-numbered terms, and 411 is in the sequence. Condition 1) is sufficient. a 2 = 112 = 3*37 + 1 and all even-numbered terms have a remainder of 1 when they are divided by 3. Since 411 = 3*137, it is not an even-numbered term. Since we don’t know any of the odd-numbered terms, condition 2) is not sufficient. Therefore, A is the answer. Answer: A

=> Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. Modifying the question: The question asks if \sqrt{17n} = a for some integer a. This is equivalent to asking if 17n = a^2 for some integer a. Since we have 1 variable ( n ) and 0 equations, D is most likely to be the answer. So, we should consider each of the conditions on their own first. Condition 1) Since 68n is the square of an integer and 68 = 4*17 , we must have 68n = 4*17*17*k^2 for some integer k , and n = 17*k^2 or 17n = 17^2*k^2 = (17*k)^2. Thus, 17n is the square of the integer 17k , and condition 1) is sufficient. Condition 2) Since \frac{n}{68} is a square of an integer and 68 = 4*17 , we have \frac{n}{68} = m^2 for some integer m , and n = 17*4*m^2 or 17n = 17^2*2^2*m^2 = (34m)^2. Thus, 17n is the square of the integer 17k , and condition 2) is sufficient. Therefore, D is the answer. Answer: D If the original condition includes “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations” etc., one more equation is required to answer the question. If each of conditions 1) and 2) provide an additional equation, there is a 59% chance that D is the answer, a 38% chance that A or B is the answer, and a 3% chance that the answer is C or E. Thus, answer D (conditions 1) and 2), when applied separately, are sufficient to answer the question) is most likely, but there may be cases where the answer is A,B,C or E.

=> Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. Visit https://www.mathrevolution.com/gmat/lesson for details. Since we have 3 variables ( a, b , and c ) and 0 equations, E is most likely the answer. So, we should consider conditions 1) & 2) together first. After comparing the number of variables and the number of equations, we can save time by considering conditions 1) & 2) together first. Conditions 1) & 2) If a = 1, b = -1, c = 3 , then we have a^2 + b^2 + c^2 = 1 + 1 + 9 = 11. If a = 2, b = -2, c = 3 , then we have a^2 + b^2 + c^2 = 4 + 4 + 9 = 17. Since both conditions together do not yield a unique solution, they are not sufficient. Therefore, E is the answer. Answer: E In cases where 3 or more additional equations are required, such as for original conditions with “3 variables”, or “4 variables and 1 equation”, or “5 variables and 2 equations”, conditions 1) and 2) usually supply only one additional equation. Therefore, there is an 80% chance that E is the answer, a 15% chance that C is the answer, and a 5% chance that the answer is A, B, or D. Since E (i.e. conditions 1) & 2) are NOT sufficient, when taken together) is most likely to be the answer, it is generally most efficient to begin by checking the sufficiency of conditions 1) and 2) when taken together. Obviously, there may be occasions on which the answer is A, B, C, or D.

=> Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. We have \frac{1}{a} > \frac{1}{b} > \frac{1}{c} , since we are given that 0 \frac{1}{b} > \frac{1}{c} > 0 , and \frac{1}{a} + \frac{1}{b} + \frac{1}{c} = 1 , we must have \frac{1}{a} + \frac{1}{a} + \frac{1}{a} = \frac{3}{a} > 1 . Therefore, a < 3 , and the answer is ‘yes’. Condition 2) is sufficient since it yields a unique answer. Therefore, D is the answer. Answer: D This question is a CMT4(B) question: condition 1) is easy to work with and condition 2) is difficult to work with. For CMT4(B) questions, D is most likely to be the answer.

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MathRevolution

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[GMAT math practice question]

(number property) If $m$ and $n$ are positive integers, what is the remainder when $12^{mn}$ is divided by $13$?

1) m=even
2) n=odd

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[quote="cuhmoon"]There are 3 different positive integers. If their average (the arithmetic mean) is 8, what are their values?
1) The largest integer is twice the smallest integer.
2) One of them is 9.

Can someone explain how is the OA for this A??

Trying to explain,
X+y+2x= 8*3
Y has to be a number between x & 2x.

To get a range and possibilities, let's assume y=0 and check for rest-
X+2x= 24, => y has to be between 8&16 such that it's greater than 8 but also satisfies our first equation; sum of 3 = 24.

Lets check;
8,y,16= doesn't satisfy sum= 24,
Again to satisfy sum = 24 let's try 7,y,14 ,y= 24-21=3 which again is not greater than smallest number 7.
Using similar logic, we can figure
5,y,10 is the only combination that gives y> smallest number 5 and to satisfy sum = 24 it may safely be assumed as 9.
One Unique combination is 5,9,10.
Hence A is the answer.

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[GMAT math practice question]

(algebra) $x, y$ and $z$ are the number of $$2$ stamps, $$3$ stamps and $$10$ stamps, respectively. What is the value of $xyz$?

1) The total number of stamps is $20$.

2) The total value of all the stamps is $$100$.

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[Math Revolution GMAT math practice question]

(number properties) $n$ is a $3$ digit integer of the form $ab6$. Is $n$ divisible by $4$?

1) $a+b$ is an even integer
2) $ab$ is an odd integer.

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[GMAT math practice question]

(Function) What is $f(g(2))$?

$1) f(x) =3x-2$

$2) g(x)=x^2$

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[Math Revolution GMAT math practice question]

(sequence) The terms of $a$ sequence are defined by an=an-2+3. Is 411 a term of the sequence?

1) a1=111
2) a2=112

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[Math Revolution GMAT math practice question]

(number properties) If $n$ is a positive integer, is $\sqrt{17n}$ an integer?

1) $68n$ is the square of an integer.
2) $\frac{n}{68}$ is the square of an integer.

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[GMAT math practice question]

(Algebra) $abc ≠ 0$. What is the value of $a^2+b^2+c^2$?

1) $a+b+c=3.$

2) $a^3+b^3+c^3=27.$

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[GMAT math practice question]

(inequality) $0 < a < b < c$. Is $a < 3$?

$1) \frac{1}{c} > \frac{1}{3}$

$2) \frac{1}{a} + \frac{1}{b} + \frac{1}{c} = 1$

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[GMAT math practice question]

(number properties) $m$ and $n$ are integers. What is the value $(-1)^{m-n} +(-1)^{m+n} +(-1)^{mn} +(-1)^{2n}$?

$1) m = n + 1$

$2) m = 3$

=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.
Visit https://www.mathrevolution.com/gmat/lesson for details.

Since we have $2$ variables ($m$ and $n$) and $0$ equations, C is most likely the answer. So, we should consider conditions 1) & 2) together first. After comparing the number of variables and the number of equations, we can save time by considering conditions 1) & 2) together first.

Conditions 1) & 2)
Since we have $m = n + 1$ and $m = 3$, we can substitute $m = 3$ into $m = n + 1$ to get $3 = n + 1$ and $n = 2.$

$(-1)^{m-n} +(-1)^{m+n} +(-1)^{mn} +(-1)^{2n}$

$=(-1)^{3-2} +(-1)^{3+2} +(-1)^{3*2} +(-1)^{2*2}$

$=(-1)^1 +(-1)^5 +(-1)^6 +(-1)^4$

$=(-1) + (-1) + 1 + 1 = 0$

Since both conditions together yield a unique solution, they are sufficient.

Since this question is an integer question (one of the key question areas), CMT (Common Mistake Type) 4(A) of the VA (Variable Approach) method tells us that we should also check answers A and B.

Condition 1)
Since $m = n + 1$, $m$ and $n$ are consecutive integers, they have different parities, which means that if $m$ is an odd integer, then $n$ is an even integer, and if $m$ is an even integer, then $n$ is an odd integer.

Case 1: $m$ is an odd integer and $n$ is an even integer.
Then, $m+n$ is an odd integer, $m – n$ is an odd integer, $mn$ is an even integer and $2n$ is an even integer.
$(-1)^{m-n} +(-1)^{m+n} +(-1)^{mn} +(-1)^{2n}$

$=(-1)^{odd} +(-1)^{odd} +(-1)^{even} +(-1)^{even}$

$=(-1) + (-1) + 1 + 1 = 0$

Case 2: $m$ is an even integer and $n$ is an odd integer.
Then, $m+n$ is an odd integer, $m – n$ is an odd integer, $mn$ is an even integer and $2n$ is an even integer.
$(-1)^{m-n} +(-1)^{m+n} +(-1)^{mn} +(-1)^{2n}$

$=(-1)^{odd}+(-1)^{odd} +(-1)^{even} +(-1)^{even}$

$=(-1) + (-1) + 1 + 1 = 0$

Since condition 1) yields a unique solution, it is sufficient.

Condition 2)

Case 1: $n$ is an even integer.
Then, $m+n$ is an odd integer, $m – n$ is an odd integer, $mn$ is an even integer and $2n$ is an even integer, since $m = 3.$

$(-1)^{m-n} +(-1)^{m+n} +(-1)^{mn} +(-1)^{2n}$

$=(-1)^{odd} +(-1)^{odd} +(-1)^{even} +(-1)^{even}$

$=(-1) + (-1) + 1 + 1 = 0$

Case 2: $n$ is an odd integer.
Then, $m+n$ is an even integer, $m – n$ is an even integer, $mn$ is an odd integer and $2n$ is an even integer.

$(-1)^{m-n} +(-1)^{m+n} +(-1)^{mn} +(-1)^{2n}$

$=(-1)^{even} +(-1)^{even} +(-1)^{odd} +(-1)^{even}$

$=1 + 1 + (-1) + 1 = 2$

Since condition 2) does not yield a unique solution, it is not sufficient.

If the question has both C and A as its answer, then A is an answer rather than C by the definition of DS questions. Also, this question is a 50/51 level question and can be solved by using the Variable Approach and the relationship between Common Mistake Type 3 and 4 (A or B).

Therefore, A is the answer.
Answer: A

Normally, in problems which require 2 equations, such as those in which the original conditions include 2 variables, or 3 variables and 1 equation, or 4 variables and 2 equations, each of conditions 1) and 2) provide an additional equation. In these problems, the two key possibilities are that C is the answer (with probability 70%), and E is the answer (with probability 25%). Thus, there is only a 5% chance that A, B, or D is the answer. This occurs in common mistake types 3 and 4. Since C (both conditions together are sufficient) is the most likely answer, we save time by first checking whether conditions 1) and 2) are sufficient, when taken together. Obviously, there may be cases in which the answer is A, B, D, or E, but if conditions 1) and 2) are NOT sufficient when taken together, the answer must be E.

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[Math Revolution GMAT math practice question]

(number property) Is the $5$-digit positive integer $abc000$ divisible by $24$?

1) The $3$-digit integer $abc$ is divisible by $8$.
2) The $3$-digit integer $abc$ is divisible by $3$.

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[GMAT math practice question]

(number properties) What is the value of $p*q$?

1) $p$ and $q$ are prime numbers

2) $q-p=3$

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[GMAT math practice question]

(Equation) $2ax - 3b = a - bx$ is an equation in terms of $x$. What is its solution?

1) $\frac{-3}{2}$ is a solution of $(b-a)x - (2a-3b) = 0$

2) $a = 3b$

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[GMAT math practice question]

(number properties) What is the greatest common divisor of positive integers $m$ and $n$?

1) $m$ and $n$ are consecutive
2) $m^2 – n^2 = m + n$

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[GMAT math practice question]

(number properties) $p$ and $q$ are different positive integers. What is the remainder when $p^2 + q^2$ is divided by $4$?

1) $p$ and $q$ are prime numbers.

2) $p$ and $q$ are not consecutive integers.

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[Math Revolution GMAT math practice question]

(number properties) If $x$ and $y$ are positive integers, is $\sqrt{15xy}$ an integer?

1) $xy$ is a multiple of $15$
2) $x$ and $y$ are prime numbers

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[GMAT math practice question]

(algebra) Let $x$ be a real number. $(a, b)$ denotes $ax+b$. What is $(1, 0)$?

$1) 3*(2,0)=(-1, 4) – (-2, -6)$

$2) (1, 0)^2 +4 = 4(1, 0)$

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Based on this guide, I may have just missed Q50. Don't have a large iced coffee right before you go into the testing center--it hits you midway through the first (Quant) section and breaks your focus!

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[GMAT math practice question]

(absolute value) If |2x|>|3y|, is x >y?

1) x>0
2) y>0

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[GMAT math practice question]

(algebra) What is $a$?

$1) 3x-[7x-{2x-(5-6x)}] = -10x+4$

$2) –a+5 = 11x$

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