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Overview of GMAT Math Question Types and Patterns on the GMAT

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New post 02 Jul 2020, 17:20
[GMAT math practice question]

(Inequalities) m is an integer where m = x + y. What is the minimum value of m?

1) 5 < x < 8.
2) -7 < y < -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.
Visit https://www.mathrevolution.com/gmat/lesson for details.

Since we have 3 variables (x, y, and m) and 1 equation, 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) together give us:
When we add the inequalities 5 < x < 8 and -7 < y < -4, we have -2 < x + y < 4 or -2 < m < 4.
Since m is an integer, we have -1 ≤ m ≤ 3.
Thus, the minimum value of m is -1.

The answer is unique, and conditions 1) and 2) together are sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Since this question is an inequality 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.

Let’s look at the condition 1). Since it doesn’t have any information regarding the variable y, the answer is not unique, and the condition is not sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Let’s look at the condition 2). Since it doesn’t have any information regarding the variable x, the answer is not unique, and the condition is not sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Both conditions 1) and 2) together are sufficient.
Therefore, C is the correct answer.
Answer: C

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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New post 05 Jul 2020, 18:22
[GMAT math practice question]

(Number Properties) F(n) denotes the units digit of a positive integer n. What is the value of F(3^8+7^15)?

A. 3
B. 4
C. 7
D. 8
E. 9

=>

The units digit of the exponents of 3 repeats 3^1 ~ 3, 3^2 ~ 9, 3^3 ~ 7, 3^4 ~ 1 every four times when multiplying by 3.
The units digit of the exponents of 4 repeats 7^1 ~ 7, 7^2 ~ 9, 7^3 ~ 3, 7^4 ~ 1 every four times when multiplying by 7.

F(3^8 + 7^15) = F(3^4 + 7^3) = F(1 + 3) = F(4) = 4.

Therefore, B is the correct answer.
Answer: B
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New post 08 Jul 2020, 17:39
[GMAT math practice question]

(Algebra) A○B denotes 1/A + B-1/A (A ≠ -B and A ≠ 0). What is the value of xy?

1) x = (1 + A) ○ (1 - A).
2) y = (1 - A) ○ (1 + A).

=>

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. We should simplify conditions if necessary.

Since we have 2 variables (x and y) 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) together give us:
x = (1 + A) ○ (1 - A) = [1 / (1 + A + 1 - A)] – [1 / (1 + A)] = [1/2] – [1 / (1 + A)] = [(1 + A) / 2(1 + A)] – [2 / 2(1 + A)] = [(1 + A - 2) / 2(1 + A)] = [(A - 1) / 2(1 + A)].
y = (1 - A) ○ (1 + A) = [1 / (1 – A + 1 + A)] – [1 / (1 - A)] = [1/2] – [1 / (1 - A)] = [(1 - A) / 2(1 - A)] – [2 / 2(1 - A)] = [(1 – A - 2) / 2(1 - A)] = -(A + 1) / 2(1 - A).
Then, we have xy = [(A - 1) / 2(1 + A)] · [-(A + 1) / 2(1 - A)] = [(A – 1)·(-A – 1)] / [4·(1 + A)·(1 – A)] = [-A2 – A + A + 1] / [4·(1 – A + A - A2] = [-A2 + 1] / [4·(1 – A2] = [1 – A2] / [4·(1 - A2] = ¼.

The answer is unique, and conditions 1) and 2) together are sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Both conditions 1) & 2) together are sufficient.

Therefore, C is the correct answer.
Answer: C

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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New post 09 Jul 2020, 17:40
[GMAT math practice question]

(Algebra) The table shows the difference in bag production at a factory between the production number of that day and that of the previous day. A positive number means the number of bags produced on that day is greater than the previous day. A negative number means the number of bags produced that day is less than the previous day. The production number on the 12th day is 42,000. How many bags were produced on the 8th day?

A. 41400
B. 41700
C. 41900
D. 42300
E. 42500

Attachment:
6.29ps.png
6.29ps.png [ 2.6 KiB | Viewed 422 times ]


=>

The number of bags produced on the 11th day is 42,000 + 300 = 42,300.
The number of bags produced on the 10th day is 42,300 - 400 = 41,900.
The number of bags produced on the 9th day is 41,900 - 500 = 41,400.
The number of bags produced on the 8th day is 41,400 + 300 = 41,700.

Therefore, B is the correct answer.
Answer: B
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New post 12 Jul 2020, 19:07
[GMAT math practice question]

(Set) Set A is given as {1, 2, 3, … , n} and n is a positive integer. What is the value of n?

1) The number of subsets of A containing both 1 and n is 16.
2) n is less than 8.

=>

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 1 variable (n) and 0 equations, D is most likely the answer. So, we should consider each condition on its own first.

Let’s look at condition 1). It tells us that set A has four elements.

Remember that the number of subsets of a set with n elements is 2n.
Since 2n = 24 = 16, we have n = 4.

The answer is unique, and the condition is sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Let’s look at condition 2). It tells us that we don’t have a unique solution since n = 6 and n = 7 are possible values.

The answer is not unique, and the condition is not sufficient, according to Common Mistake Type 2, which states that the number of answers must be only one.

Condition 1) ALONE is sufficient.

Therefore, A is the correct answer.
Answer: A

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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New post 14 Jul 2020, 17:34
[GMAT math practice question]

(Equation) What is the value of a?

1) The equation x/3 + a = x/2 - x - 18/6 in terms of x has no solution.
2) a 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.
Visit https://www.mathrevolution.com/gmat/lesson for details.

Since we have 1 variable (a) and 0 equations, D is most likely the answer. So, we should consider each condition on its own first.

Let’s look at the condition 1). It tells us that a could be any value other than 3.

x/3 + a = x/2 – x - 18/6
⇔ x/3 + a = x/3 + 3
⇔ a = 3.

It means if a = 3, the equation has an infinite number of solutions, and if a ≠ 3, the equation has no solution. Thus, a can be any value other than 3.

The answer is not unique, and the condition is not sufficient, according to Common Mistake Type 2, which states that the number of answers must be only one.

Let’s look at the condition 2). It tells us that a does not have a unique solution.
Any integer can be the value of a.

The answer is not unique, and the condition is not sufficient, according to Common Mistake Type 2, which states that the number of answers must be only one.

Conditions 1) & 2) together tell us that we don’t have a unique solution, as a can be any integer other than 3.

The answer is not unique, and the conditions 1) and 2) together are not sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Both conditions 1) & 2) together are not sufficient.

Therefore, E is the correct 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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New post 16 Jul 2020, 18:02
[GMAT math practice question]

(Absolute Value) a and b satisfy a – b > 0 and ab < 0. Which of following is the expression of |a| + |b|?

A. a + b
B. a - b
C. –a + b
D. –a - b
E. b - a

=>

Since ab < 0, a and b have different signs.
Since a – b > 0, we have a > b.
Since a and b have different signs with a > b, a is positive, and b is negative.

Then |a| + |b| = a + (-b) = a – b.

Therefore, B is the correct answer.
Answer: B
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New post 19 Jul 2020, 18:24
[GMAT math practice question]

(Set) Among 100 employees, how many employees like both apples and bananas?

1) 53 employees like apples.
2) 72 employees like bananas.

=>

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.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. We should simplify conditions if necessary.

Attachment:
7.13ds(a).png
7.13ds(a).png [ 10.41 KiB | Viewed 271 times ]



A and B are sets of employees who like apples and banana, respectively. When we set this question up as the above Venn Diagram, we have x + y + z + w = 100.

Since we have 4 variables (x, y, z and w) and 1 equation (x + y + z + w = 100), 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.
The question asks what the value of y is.

Conditions 1) & 2) together give us that they are not sufficient together.

Since 53 employees like apples, we have x + y = 53 from condition 1).
Since 72 employees like bananas, we have y + z = 72 from condition 2).

If x = 20, z = 39, w = 8, then we have y = 33.
If x = 21, z = 40, w = 7, then we have y = 32.

The answer is not unique, and both conditions 1) and 2) together are not sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Both conditions 1) & 2) together are not sufficient.

Therefore, E is the correct 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.
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New post 22 Jul 2020, 17:27
[GMAT math practice question]

(Function) a and b are non-zero real numbers. In which quadrant is point (a, b) on located?

1) y = ax and y = b/x have an intersection.
2) a + b > 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.
Visit https://www.mathrevolution.com/gmat/lesson for details.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. We should simplify conditions if necessary.

Since we have 2 variables (a and b) 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) together give us:

Since a and b have the same parities in order for y = ax and y = b/x to have an intersection, we have ab > 0 from condition 1).

Since we have a + b > 0 from condition 2), we have a > 0 and b > 0 when we consider both conditions together.

Then point (a, b) is in the first quadrant.

The answer is unique, and conditions 1) and 2) together are sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Both conditions 1) & 2) together are sufficient.

Therefore, C is the correct answer.
Answer: C

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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New post 23 Jul 2020, 17:45
[GMAT math practice question]

(Geometry) Quadrilaterals □ADEB and □ACGF are squares with the same sides. What is the measure of the angle ∠x?

A. 45° B.55° C. 75° D. 80° E. 90°

Attachment:
7.13PS.png
7.13PS.png [ 10.46 KiB | Viewed 206 times ]


=>

Since AB = AC = AD = AF and ∠DAC = ∠BAF, triangles ADC and ABF are congruent. Then we have ∠ADC = ∠ABF.
∠x = 180° - ∠DHB = 180° – (360° - ( ∠E + ∠EDH + ∠EBH ))
= 180° – ( 36° – ( 90° + ∠EDA - ∠ADC + ∠EBA + ∠ABF ) )
= 180° – ( 360° – ( 90° + 90° - ∠ADC + 90° + ∠ADC ) )
= 180° – ( 360° – 270° ) = 90°

Therefore, E is the correct answer.
Answer: E
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New post 26 Jul 2020, 18:18
[GMAT math practice question]

(Arithmetic) a = 4/39. What is the value of 10^6a - a?

A. 10,2500
B. 102,510
C. 102,555
D. 102,564
E. 102,573


=>

10^6a - a = a(10^6 - 1) = 4/39 · 999,999 = 4/13 · 333,333
= 4 · 25641 = 102,564

Therefore, D is the correct answer.
Answer: D
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New post 28 Jul 2020, 17:41
[GMAT math practice question]

(Number Properties) m and n are positive integers. What is the value of mn?

1) 2.03(n/m) = (0.3)^2
2) m and n are relatively prime integers.

=>

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) together tell us that m and n are relatively prime integers with 203n = 9m.

We have 203/100*n/m=(3/10)^2=9/100 or 203n = 9m from condition 1).
Since m and n are relatively prime, we have m = 203 and n = 9.

The answer is unique, and conditions 1) and 2) together are sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

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.

Let’s look at condition 1). It tells us that 203n = 9m.
If m = 203 and n = 9, then we have mn = 1827.
If m = 406 and n = 18, then we have mn = 7308.

The answer is not unique, and the condition is not sufficient, according to Common Mistake Type 2, which states that the number of answers must be only one.

Let’s look at condition 2). It tells us that m and n are relative primes.
If m = 203 and n = 9, then we have mn = 1827.
If m = 2 and n = 3, then we have mn = 6.

The answer is not unique, and the condition is not sufficient, according to Common Mistake Type 2, which states that the number of answers must be only one.

Both conditions 1) & 2) together are sufficient.

Therefore, C is the correct answer.
Answer: C

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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New post 30 Jul 2020, 17:49
[GMAT math practice question]

(Function) f is a function mapping from {1, 2, 3} to {1, 2, 3, 4, 5}. x + f(x) is odd. How many possible cases of f(x) do we have?

A. 9
B. 10
C. 11
D. 12
E. 13

=>

If x is an odd number, then f(x) is an even number.
If x is an even number, then f(x) is an odd number.
Then the possible values of f(1) and f(3) are 2 and 4. The number of possible cases for f(1) and f(3) is 2.
The possible values of f(2) are 1, 3, and 5. The number of possible cases for f(2) = 3.

Thus. the number of possible cases for the function f(x) is 2·2·3 = 12.

Therefore, D is the correct answer.
Answer: D
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Re: Overview of GMAT Math Question Types and Patterns on the GMAT  [#permalink]

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New post 03 Aug 2020, 18:17
[GMAT math practice question]

(Number Properties) x, y, and z are positive integers and z < y < x. What is the value of 1/x + 1/y + 1/z?
1) 1/x + 1/y + 1/z is an integer.
2) x = yz and y and z are consecutive integers and 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.
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 to be the answer. Let’s look at both conditions together. However, since the value of condition (1) is equal to the value of condition (2), by Tip 1, we get D as the most likely answer. Let’s look at each condition separately

Let’s look at the condition 1). It tells us that since we have z ≥ 1, y ≥ 2, and x ≥ 3, we have 1/z ≤ 1, 1/y ≤ 1/2, and 1/x ≤ 1/3.
1/x + 1/y + 1/z ≤ 1 + 1/2 + 1/3 = 1 + 3/6 + 2/6 = 1 + 5/6 = 6/6 + 5/6 = 11/6 < 2 from condition 1).
Since the unique positive integer less than 2 is 1, we have 1/x + 1/y + 1/z = 1.

The actual values of x, y, and z are 6, 3, and 2, respectively.

The answer is unique, so the condition is sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Let’s look at the condition 2). It tells us that

Since 2 and 3 are unique consecutive integers and prime numbers, we have y = 3 and z = 2.
If x = 6, y = 3 and z = 2, then 1/x + 1/y + 1/z = 1/6 + 1/3 + 1/2 = 1/6 + 2/6 + 3/6 = 6/6 = 1.

The answer is unique, so the condition is sufficient according to Common Mistake Type 2, which states that the number of answers must be only one.

Each condition ALONE is sufficient.

Therefore, D is the correct answer.
Answer: D

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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Re: Overview of GMAT Math Question Types and Patterns on the GMAT   [#permalink] 03 Aug 2020, 18:17

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Overview of GMAT Math Question Types and Patterns on the GMAT

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