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.

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10 Apr 2017, 18:46

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What is the range of 25 consecutive even numbers?

A. 44
B. 46
C. 48
D. 50
E. 52

==> The number of consecutive even numbers=(The last number-the first number)/2 +1=range/2+1, so from range/2+1=25, range/2=25-1=24, you get range=2(24)=48. Therefore, the answer is C.
Answer: C

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If x and y are positive integers, is x divisible by y?

1) x is divisible by 6
2) y is divisible by 6

==> In the original condition, there are 2 variables (x,y) and in order to match the number of variables to the number of equations, there must be 2 equations. Since there is 1 for con 1) and 1 for con 2), C is most likely to be the answer. By solving con 1) and con 2), (x,y)=(6,6) yes, but (x,y)=(6,12) no, hence it is not sufficient.

Therefore, the answer is E.
Answer: E

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If (4/9)÷n=3/5, n=?

A. 20/27
B. 27/20
C. 10/9
D. 9/10
E. 9/4

==>(4/9)÷n=3/5 -> (4/9)(1/n)=3/5. And 4/9n=3/5 -> n=(4/9)(5/3)=20/27.

Hence, the answer is A.
Answer: A

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2x+3y=?

1) x=6
2) 4x+6y=18

==> In the original condition, you get 2x+3y=?. For con 2), if you divide both sides by 2, you get 2x+3y=9, hence it is unique and sufficient.

Therefore, the answer is B.
Answer: B

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If 3 juniors from 8 juniors are selected at random to make a committee, how many cases are possible?

A. 8
B. 28
C. 35
D. 42
E. 56

==> In general, you solve probability questions using nCr, a combination. In other words, from 8C3=56, the answer is E.
Answer: E

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If $x^{-2}+x^{-1}=0$, x=?

A. -1
B. 0
C. 1
D. 0, 1
E. -1, 0

==> If you multiply $x^2$ on both sides, you get 1+x=0, x=-1. The answer is A.
Answer: A

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If b≠0, |a/b|=a/b, is b>0?

1) a>0
2) a+b>0

==> If you modify the original condition and the question, in order to satisfy |a/b|=a/b, you must get a/b≥0, and if you multiply b^2 on both sides, from (b^2)a/b≥(b^2)0, you get ab≥0. Since the question is b>0? becomes a≥0?, con 1) is yes and sufficient. For con 2), using CMT 4 (B: if you get A or B too easily, consider D), you only get ab≥0 and a+b>0 when a>0 and b>0, hence yes, it is sufficient.

Therefore, the answer is D.
Answer: D

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When n and k are positive integers, what is the greatest common divisor of n+k and n?

1) n=2
2) k=1

==> In the original condition, there are 2 variables, and in order to match the number of variables to the number of equations, there must be 2 equations. Since there is 1 for con 1) and 1 for con 2), C is most likely to be the answer. By solving con 1) and con 2), you get n+k=2+1=3 and n=2, and GCD(3,2)=1, hence it is unique and sufficient. Therefore, the answer is C. However, this is an integer question, one of the key questions, so you apply CMT 4 (A: if you get C too easily, consider A or B).
For con 1), k is unknown hence it is not sufficient.
For con 2), if k=1, n+k(=n+1) and n becomes 2 consecutive integers, so always GCD=1, hence it is unique and sufficient.

Therefore, the answer is B, not C.
Answer: B

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If x and y are positive, is (y/x)+(x/y)>2?

1) x>y
2) x>1>y

==> If you modify the original condition and the question, even if you multiply xy on both sides, you get xy>0, hence the inequality sign doesn’t change. Thus, you get is (y/x)+(x/y)>2?, or $y^2+x^2>2xy?$, or $y^2+x^2-2xy>0$?, or $(x-y)^2>0$?, or x≠y?. From con 1) = con 2), it is always yes and sufficient.

The answer is D.
Answer: D

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When a certain coin is flipped, the probability that the coin will land on head or tail is 1/2 each. If the coin is flipped 4 times, what is the probability that it will land on tail at least twice on 4 flips?

A. 3/8
B. 1/16
C. 1/2
D. 5/8
E. 11/16

==> In general, you solve probability questions using nCr combination. In other words, from TTHH, there are (4!/2!/2!)=6 possibilities, so you get (1/2)(1/2)(1/2)(1/2)*6=3/8. From TTTH, there are (4!/3!)=4 possibilities, so you get (1/2)(1/2)(1/2)(1/2)*4=1/4. From TTTT, there is only 1 possibility, so you get (1/2)(1/2)(1/2)(1/2)=1/16 and (3/8)+(1/4)+(1/16)=(6+4+1)/16=11/16. The answer is E.
Answer: E

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There are a lot of products. Is the standard deviation of the prices of the products less than $60?

1) The median value of their price is $100
2) The range of their price is $110

==> If you modify the original condition and the question, you get standard deviation(d)≤range/2. Then, from d≤range/2=$110/2=$55<$60, it is always yes and sufficient.

Therefore, the answer is B.
Answer: B

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When a/b=1.2, (a-b)/(a+b)=?

A. 1/15
B. 1/11
C. 1/9
D. 3/8
E. 1/3

==> From a/b=1.2=6/5, if you substitute a=6 and b=5, you get (a-b)/(a+b)=(6-5)/(6+5)=1/11.

Therefore, the answer is B.
Answer: B

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If nk≠0, n is what percent of k?

1) k=0.2n
2) (k+n)/n=1.2

==> If you modify the original condition and the question, from n=(some)(1/100)k, you get some=100(n/k). However, con 1) = con 2), so you get some=100(0.2)=20, hence it is unique and sufficient.

Therefore, the answer is D.
Answer: D

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If the sum of the annual salary of n persons is $x and the monthly salary per person is $y, what is the value of n in terms of x and y?

A. $x/12y
B. $12x/y
C. $12xy
D. $12y/x
E. $xy/12

==> If the annual salary per person: s, you get ns=x, s=12y. If you substitue this, you get n(12y)=x, n=x/12y.

Therefore, the answer is A.
Answer: A

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If n is the product of 3 consecutive integers, which of the following must be true?

I. a multiple of 2 II. a multiple of 3 III. a multiple of 4

A. I only
B. II only
C. III only
D. I and II only
E. II and III only

==> From n=m(m+1)(m+2) , where m=integer, the product of 3 consecutive integers is always a multiple of 6. Thus, I and II is always true. For III, if m=1, from n=(1)(2)(3)=6, it is not a multiple of 4, hence it is false.

Therefore, the answer is D.
Answer: D

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If the average (arithmetic mean) of set A is 10,000 and the average (arithmetic mean) of set B is 10,000, what is the range of set A and set B combined?

1) The range of set A is 6,000
2) The range of set B is 3,000

==> If you modify the original condition and the question, since there are 2 sets, set 1’s range=set 1’s Max-set 1’s min, and set 2’s range=set 2’s Max-set 2’s min. Thus, there are 6 variables and 2 equations, and in order to match the number of variables to the number of equations, there must be 4 more equations. Since there is 1 for con 1) and 1 for con 2), E is most likely to be the answer. By solving con 1) and con 2), the max and the min when combined is unknown, hence it is not sufficient. Therefore, the answer is E.
Answer: E

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If x+y=3 and $x^2+y^2=7$, then xy=?

A. -2
B. -1
C. 0
D. 1
E. 2

==> You get $(x+y)^2=x^2+y^2+2xy$, and if you substitute this, from $3^2=7+2xy$, you get 2xy=2, and xy=1.

Therefore, the answer is D.
Answer: D

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(1/7)+(1/8)+(1/9) is in between?

A. (1/6) and (1/5)
B. (1/5) and (1/4)
C. (1/4) and (1/3)
D. (1/3) and (1/2)
E. (1/2) and 1

==>The sum of consecutive reciprocal numbers is decided by the first and the last number. In other words, you get
(1/9)+(1/9)+(1/9)< (1/7)+(1/8)+(1/9)< (1/7)+(1/7)+(1/7), and if you reorganize this, from
=1/3=3/9=(1/9)+(1/9)+(1/9)<(1/7)+(1/8)+(1/9)<(1/7)+(1/7)+(1/7)=3/7<3/6=1/2, you get between (1/3) and (1/2).

The answer is D.
Answer: D

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11 May 2017, 18:18

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Set S has six numbers and their average (arithmetic mean) is 32. What is the median of the numbers?

1) The six numbers are greater than or equal to 31
2) There is “37” in set S

==> In the original condition, there are 6 variables and 1 equation. In order to match the number of variables to the number of equations, there must be 5 more equations. Since there is 1 for con 1) and 1 for con 2), E is most likely to be the answer. By solving con 1) and con 2), you get
31, 31, 31, 31, 31, 37, and so the median=31+310/2=31, hence it is unique and sufficient.

The answer is C.
Answer: C

MathRevolution

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Joined: 16 Aug 2015

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14 May 2017, 18:35

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If a prime number m can be expressed as $2^n-1$, where n is a positive integer, which of the following can be the value of m?

A. 11
B. 15
C. 31
D. 63
E. 97

==> If n=5, you get $2^5-1=31$. The answer is C.
Answer: C

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