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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
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GPA: 3.82

Re: Math Revolution Approach (DS)
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03 Aug 2018, 02:05
[ Math Revolution GMAT math practice question] Is 0 between x and y? 1) xy>0 2) x^2y^2>0 => 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. If we modify the question, it asks if xy < 0. Since the two conditions do not give us enough information to determine the sign of xy, both conditions together are not sufficient, and the answer is E. Since we have 2 variables (x and y) and 1 equation, D is most likely to be the answer. So, we should consider each of the conditions on its own first. Conditions 1) & 2) If x = 2 and y = 1, then 0 is between x and y. If x = 2 and y = 1, then 0 is not between x and y. Since we don’t have a unique solution, both conditions together are not sufficient. Therefore, E is the answer. Answer: E 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 Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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05 Aug 2018, 19:04
[ Math Revolution GMAT math practice question] If the average (arithmetic mean) height of Bob, John and Tom is 180 cm, what is their median height? 1) Bob’s height is 175cm. 2) John’s height is 180cm. => 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. When we have 3 numbers, if one of them is equal to their average, then it is also equal to their median. Thus, condition 2) is sufficient. Therefore, B is the answer. Answer: B
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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05 Aug 2018, 19:05
[ Math Revolution GMAT math practice question] When a positive integer n is divided by 3, what is the remainder? 1) When n is divided by 5, the remainder is 2 2) When n is divided by 6, the remainder is 2 => 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. Since the divisor (6) of condition 2) is a multiple of the divisor (3) of the question, condition 2) is sufficient. When we encounter questions related to remainders, plugging in numbers is suggested. Condition 1) If n = 2, then the remainder when n is divided by 3 is 2. If n = 7, then the remainder when n is divided by 3 is 1. Since we don’t have a unique solution, condition 1) is not sufficient. Condition 2) The possible values of n are n = 2, 8, 14, 20, … All of these values have a remainder of 2 when they are divided by 3. Thus, condition 2) is sufficient. Therefore, B is the answer. Answer: B
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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08 Aug 2018, 02:09
[ Math Revolution GMAT math practice question] a, b, c, d, e and f are integers. Is their median greater than their average (arithmetic mean)? 1) a<b<c<d<e<f 2) ba=dc=fe => 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. Since we have 6 variables (x, y and z) 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. If a = 1, b = 2, c =5, d = 6, e = 7, f = 8, we have a median of 5.5 and an average of 29/6. The median is greater than the average, and the answer is “yes”. If a = 1, b = 2, c =3, d = 4, e = 5, f = 6, we have a median of 3.5 and an average of 3.5. The median is not greater than the average, and the answer is “no”. Since we don’t have a unique solution, both conditions are not sufficient, when considered together. . Therefore, the answer is E. 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.
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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09 Aug 2018, 01:29
[ Math Revolution GMAT math practice question] If n is a 2digit positive integer and its tens digit is 4 times its units digit, what is the value of n? 1) The tens digit of n is 8. 2) The sum of the tens digit and the units digit of n is 2digit integer. => 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. n = 10a + b and a = 4b The possible pairs ( a, b ) are ( 4, 1 ) and ( 8, 2 ) by the original condition. Thus, n = 41 or n = 82. Since we have 3 variables and 2 equations, D is most likely to be the answer. So, we should consider each of the conditions on its own first. Condition 1) Since a = 8, we must have n = 82. Thus, condition 1) is sufficient. Condition 2) Since 4 + 1 = 5 is not a 2digit integer and 8 + 2 = 10 is a 2digit integer, n = 82. Thus, 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.
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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13 Aug 2018, 06:22
[ Math Revolution GMAT math practice question] If a, b, and c are consecutive 2digit positive integers in that order, and a+b+c is a multiple of 10, what is the value of c? 1) a is a prime number 2) c is a prime number => 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. Since a = b – 1 and c = b + 1, we have a + b + c = ( b – 1 ) + b + ( b + 1 ) = 3b is a multiple of 10 and b is a multiple of 10. Thus, the possible triples ( a, b, c ) are ( 19, 20, 21 ), ( 29, 30, 31 ), ( 39, 40, 41 ), ( 49, 50, 51 ), ( 59, 60, 61 ), ( 69, 70, 71 ), ( 79, 80, 81 ) and ( 89, 90, 91 ). Since we have 3 variables and 2 equations ( a = b – 1, c = b + 1), D is most likely to be the answer. So, we should consider each of the conditions on their own first. Condition 1) The triples in which a is a prime number are ( 19, 20, 21 ), ( 29, 30, 31 ), ( 59, 60, 61 ), ( 79, 80, 81 ) and ( 89, 90, 91 ). Thus, c could be 21, 31, 61, 81 or 91. Since we don’t have a unique solution, condition 1) is not sufficient. Condition 2) The triples in which c is a prime number are ( 29, 30, 31 ), ( 39, 40, 41 ), ( 59, 60, 61 ), ( 69, 70, 71 ) and ( 89, 90, 91 ). Thus, c could be 31, 41, 61, 71 or 91. Since we don’t have a unique solution, condition 2) is not sufficient. Conditions 1) & 2): The triples in which both a and c are prime numbers are: ( 29, 30, 31 ), ( 59, 60, 61 ) and ( 89, 90, 91 ). Thus, c could be 31, 61 or 91. Since we don’t have a unique solution, both conditions are not sufficient, when considered together. Therefore, E is the answer. Answer: E 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.
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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13 Aug 2018, 06:25
[ Math Revolution GMAT math practice question] x ≠ 0. Is x^2>x^4? 1) x^2<1 2) x^2<2x => 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. x^2>x^4 => x^4  x^2 < 0 => x^2 ( x^2 – 1 ) < 0 => ( x^2 – 1 ) < 0 => ( x + 1 )( x – 1 ) < 0 => 1 < x < 1 This is equivalent to condition 1). Thus, condition 1) is sufficient. Condition 2) x^2<2x => x^2  2x < 0 => x(x – 2) < 0 => 0 < x < 2 In inequality questions, the law “Question is King” tells us that if the solution set of the question includes the solution set of the condition, then the condition is sufficient However, the solution set of the question 1 < x < 1 does not include the solution set of the condition, 0 < x < 2. Thus, condition 2) is not sufficient. Therefore, A is the answer.
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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15 Aug 2018, 07:45
[ Math Revolution GMAT math practice question] If the average (arithmetic mean) of 3 integers x, y, z is 10, what is the value of z? 1) x=1 2) x=5y => 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 original condition gives ( x + y + z ) / 3 = 10 or x + y + z = 30. Rearranging yields z = 30 – ( x + y ). Condition 2) gives x + y = 5, so condition 2) is sufficient . Condition 1) is not sufficient since it gives no information about the value of y. Therefore, B is the answer. Answer: B
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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16 Aug 2018, 08:49
[ Math Revolution GMAT math practice question] Is ab>bc? 1) abc=0 2) a>c => 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. When we modify the question, ab > bc is equivalent to ab – bc > 0 or b(ac) > 0. Even though we know a – c > 0 from condition 2), we don’t know if b is positive or negative. Thus, both conditions together are not sufficient. Conditions 1) & 2): If a = 1, b =1 and c = 0, then ab > bc and the answer is ‘yes’. If a = 1, b =1 and c = 0, then ab < bc and the answer is ‘no’. Since we don’t have a unique solution, both conditions together are not sufficient. Therefore, E is the answer. Answer: E
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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17 Aug 2018, 02:27
[ Math Revolution GMAT math practice question] What is the remainder when 2^n is divided by 10? 1) n is a positive multiple of 2 2) n is a positive multiple of 4 => 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 remainder when 2^n is divided by 10 is the units digit of 2^n. Now, 2^1 = 2, 2^2 = 4, 2^3 = 8, 2^4 = 16, and 2^5 = 32. So, the units digits of 2^n have period 4: They form the cycle 2 > 4 > 8 > 6. Thus, 2^n has the units digit of 6 when n is a multiple of 4. Condition 2) is sufficient. Condition 1) If n = 4, then 2^n = 2^4 = 16 has the units digit of 6. If n = 2, then 2^n = 2^2 = 4 has the units digit of 4. Since we don’t have a unique solution, condition 1) is not sufficient. Therefore, B is the answer. Answer: B
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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19 Aug 2018, 18:42
[ Math Revolution GMAT math practice question] If x, y, and z are positive integers, x=? 1) y=x+1 and z=x+3 2) x, y, and z are prime numbers => 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. Since we have 3 variables (x, y and z) 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) Since y = x + 1, z = x + 3 and x, y, z are prime numbers, the only possibility is that x = 2, y = 3, and z = 5 because if x is an odd number, then y and z are two different even numbers, which cannot both be prime numbers. Thus, both conditions together 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) There are many different possible values for x, y and z, including x = 1, y = 2, z = 4 and x = 2, y = 3, z = 5. Therefore, we don’t have a unique solution, and condition 1) is not sufficient. Condition 2) There are many different possibly values for x, y and z, including x = 2, y = 3 and z = 5, and x = 3, y = 5 and z = 7. So, we don’t have a unique solution, and condition 2) is not sufficient. 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.
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"



Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6046
GPA: 3.82

Re: Math Revolution Approach (DS)
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19 Aug 2018, 18:44
[ Math Revolution GMAT math practice question] Is n an integer? 1) 3n is an integer 2) 4n is an integer => 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. Condition 1) If n = 1, the answer is ‘yes’. If n = 1/3, the answer is ‘no’. Since we don’t have a unique solution, condition 1) is not sufficient. Condition 2) If n = 1, the answer is ‘yes’. If n = 1/4, the answer is ‘no’. Since we don’t have a unique solution, condition 2) is not sufficient. Conditions 1) & 2) Since n = 4n – 3n is a difference of two integers, n is also an integer. Conditions 1) and 2) are sufficient, when considered together. Therefore, C is the answer. Answer: C 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.
_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The oneandonly World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only $99 for 3 month Online Course" "Free Resources30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons  try it yourself"




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