GMAT Math : GMAT Quantitative Reasoning

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #442 : Arithmetic

Define an operation  on the integers as follows:

If both  and  are odd, then .

If both  and  are even, then .

If  is odd and  is even, or vice versa, then .

Add  to . What is the sum?

Possible Answers:

Correct answer:

Explanation:

Both  and  can be calculated using the definition of  for the case of exactly one of  and  being odd and one being even:

.

Add: 

Example Question #46 : Understanding Real Numbers

Define an operation  on the integers as follows:

If both  and  are prime, then .

If neither  nor  is prime, then .

If exactly one of   and  is prime, then .

Multiply  by . What is the product?

Possible Answers:

Correct answer:

Explanation:

A prime number has exactly two factors, 1 and the number itself.

Neither 6 nor 1 is a prime number; 1 has only one factor and is not considered to be prime, and 6 has more than two factors - 1, 2, 3, and 6. Therefore,  can be evaluated using the defintion of  for two numbers whose absolute values are not prime:

2 and 3 are prime numbers, since each has exactly two factors, 1 and the number itself. Therefore,  can be evaluated using the defintion of  for two numbers whose absolute values are prime:

The product is 

Example Question #2001 : Problem Solving Questions

Define an operation  on the integers as follows:

If both  and  are prime, then .

If neither  nor  is prime, then .

If exactly one of   and  is prime, then .

Subtract  from . What is the result?

Possible Answers:

Correct answer:

Explanation:

2 is a prime number, since 2 has only two factors, 1 and 2 itself. 50 is not a prime number, since 50 has other factors, such as 2.  can be evaluated using the definition of  for exactly one of  and  prime:

 

Neither 4 nor 25 are prime, since each has factors other than 1 and itself; for example,  and  can be evaluated using the definition of  for neither  nor  prime:

The difference:

Example Question #2001 : Problem Solving Questions

 is the additive inverse of . Which of the following expressions is equivalent to 

for all values of the variables?

Possible Answers:

Correct answer:

Explanation:

If  is the additive inverse of , then 

, or, equivalently,

By way of substitution and the identity property of addition,

Example Question #49 : Understanding Real Numbers

Define an operation  on the integers as follows:

If both  and  are prime, then .

If neither  nor  is prime, then .

If exactly one of   and  is prime, then .

Evaluate .

Possible Answers:

Correct answer:

Explanation:

17 and 13 are both prime numbers, since each has exactly two factors - 1 and the number itself. Therefore, we first evaluate  using the definition of  for  and  both prime:

Therefore, . 7 is also prime, since its only two factors are 1 and 7 itself. 30, however, is not prime, since 30 has factors other than 1 and itself - for example, . Therefore,  is evaluated using the definition of  for exactly one of  and  prime:

, the correct response.

Example Question #50 : Understanding Real Numbers

Define an operation  on the integers as follows:

If both  and  are prime, then .

If neither  nor  is prime, then .

If exactly one of   and  is prime, then .

Which of the following expressions is the greatest of the five?

Possible Answers:

Correct answer:

Explanation:

Of the integers shown in the five choices, the following are primes, since they have exactly two factors, 1 and the number itself:  2, 5.

1 is not consdered to be a prime, having exactly one factor (1). Also, 4, 10, 20, 25, 50, and 100 are not primes, since each has at least one factor other than 1 and itself.

  and can both be evaluated using the definition of for exactly one of and prime - that is, by multiplying the numbers:

Each of , , and  can be evaluated using the definition of for neither of and prime - that is, by adding the numbers:

The greatest of the five expressions is .

 

Example Question #2001 : Problem Solving Questions

Consider the following set of numbers:

85, 87, 87, 82, 89

What is the range?

Possible Answers:

Correct answer:

Explanation:

The range is the difference between the maximum and minimum value.

Example Question #1 : Descriptive Statistics

What is the range for the following data set:

Possible Answers:

Correct answer:

Explanation:

The range is the highest value number minus the lowest value number in a sorted data set:

We need to sort the data set:

Example Question #2 : Descriptive Statistics

What is the range for the following set:

Possible Answers:

Correct answer:

Explanation:

The range is the difference between the highest and lowest number.

First sort the set:

Example Question #1 : Descriptive Statistics

Below is the stem-and-leaf display of a set of test scores.

What is the range of this set of scores?

Possible Answers:

Correct answer:

Explanation:

The range of a data set is the difference of the highest and lowest scores,

The numbers in the "stem" of this display represent tens digits of the test scores, and the numbers in the "leaves" represent the units digits. The highest and lowest scores represented are 87 and 42, so the range is their difference: .

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