GMAT Math : GMAT Quantitative Reasoning

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #3121 : Gmat Quantitative Reasoning

Is a whole number a perfect square?

Statement 1: Its last digit is 9.

Statement 2: It falls between 160 and 170 inclusive.

Possible Answers:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

Statement 1 alone does not answer the question, since some integers ending in 9 are perfect squares (9, 49) and some are not (29, 39).

Statement 2 alone does not answer the question, since of the numbers in that range, only 169 is a perfect square (of 13).

From both statements together, however, it follows that the number in question is 169, which, as just stated, is the square of 13.

Example Question #3122 : Gmat Quantitative Reasoning

I am thinking of two distinct prime numbers. What are they?

Statement 1: Both are between 50 and 60.

Statement 2: Their sum is 112.

Possible Answers:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Correct answer:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Explanation:

Statement 1 is a giveaway; the only prime numbers between 50 and 60 are 53 and 59.

Statement 2 is not a giveaway, though, since there are at least two sums of primes equal to 112:

 and 

Example Question #3123 : Gmat Quantitative Reasoning

Is a positive integer  a prime number or a composite number?

Statement 1: 

Statement 2: 

Possible Answers:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

From Statement 1 it follows that  is a multiple of 5, but it does not answer the question by itself; 5 is prime, but the other multiples of 5 are composite. Similarly, from Statement 2 it follows that  is a multiple of 7, but, 7 is prime and the other multiples of 7 are composite.

If we can assume both statements, then, since 5 and 7 are relatively prime, it follows that  is a multiple of both 5 and 7; since  now has at least four factors (1,5, 7, and 35),  is composite.

Example Question #28 : Arithmetic

Is the product of three positive integers divisible by 4?

Statement 1: The three integers are consecutive.

Statement 2: Two of the integers are even.

Possible Answers:

EITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Correct answer:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Explanation:

Statement 1 is not enough to answer the question. For example, the integers can be 3, 4, and 5, the product of which is 60, which is divisible by 4; or, the integers can be 5, 6, and 7, the product of which is 210, which is not divisible by 4. 

From Statement 2, however, it can be inferred that the product is divisible by 4. If two of the integers are even, the two can be written as  and  for some integers . If we call the third integer , the product is , and the product must be divisible by 4.

Example Question #3123 : Gmat Quantitative Reasoning

Is the product of three integers divisible by 6?

Statement 1: The three integers are consecutive.

Statement 2: One integer is even and two are odd.

Possible Answers:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Correct answer:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Explanation:

Any group of three consecutive integers must include at least one multiple of 3 and at least one even number (multiple of 2). Therefore, if Statement 1 is assumed, 2 and 3 both divide the product of the integers and, subsequently, so does 6. 

Statement 2 is not enough, however - for example, the product of 3, 4, and 5 is 60, a multiple of 3, but the product of 4, 5, and 7 is 140, not a multiple of 3.

Example Question #3124 : Gmat Quantitative Reasoning

The triangle, the square, and the circle are replaced with three (not necessarily different) digits to form a six-digit integer. 

Is 4 a factor of this integer?

Statement 1: The square and the triangle are replaced by the same digit.

Statement 2: The circle is replaced by a 5.

Possible Answers:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Correct answer:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Explanation:

The only criterion for a number to be divisible by 4 is that the last two digits must form a number divisible by 4. This makes Statement 1 unhelpful. Statement 2, however, proves the number to not be divisible by 4, since 58 is not a multiple of 4.

Example Question #31 : Arithmetic

The four shapes are replaced below with four (not necessarily different) digits to form a six-digit integer.

Is this integer divisible by 11?

Statement 1: The circle and the triangle are replaced with the same digit.

Statement 2: The square and the diamond are replaced with the same digit.

Possible Answers:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

For a number to be divisible by 11, the alternating sum of its digits must be divisible by 11. We do not have enough information from either statement to tell us one way or the other. 

Assume both statements are true. Let  be the digit that replaces the circle and the triangle; let  be the digit that replaces the square and the diamond. Then the alternating sum is

,

which is divisible by 11. Therefore, the resulting number is also divisible by 11.

Example Question #32 : Properties Of Integers

Below is a six-digit number with its last digit replaced by a square. What is that digit?

Statement 1: The number is divisible by 11.

Statement 2: The number is divisible by 3.

Possible Answers:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Correct answer:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Explanation:

Let  be the missing digit.

If we assume only Statement 1, then the absolute value alternating sum of the digits must be a multiple of 11. That is:

  is a multiple of 11. The only positive value of  that does this is , which makes .

If we assume only Statement 2, then the sum of the digits must be a multiple of 3. That is,

 is a multiple of 3. This happens if , so Statement 2 only narrows the last digit down to three possibilities.

Example Question #33 : Properties Of Integers

For Data Sufficiency questions, select either A, B, C, D, E based on the following rubric:

  • A) statement 1 alone is sufficient, but statement 2 alone is not sufficient to answer the question
  • (B) statement 2 alone is sufficient, but statement 1 alone is not sufficient to answer the question
  • (C) both statements taken together are sufficient to answer the question, but neither statement alone is sufficient
  • (D) each statement alone is sufficient
  • (E) statements 1 and 2 together are not sufficient, and additional data is needed to answer the question

A 2 ft rope is cut into three pieces.  What is the length of each piece of rope?

1. One piece is 8 inches long.

2. The sum of the lengths of two of the pieces is 4 greater than the length of the third piece.

Possible Answers:

A

C

B

D

E

Correct answer:

C

Explanation:

We have 3 pieces of rope, and their lengths all add to 2 ft, or 24 inches.  Let X, Y, and Z represent the three lengths.  Our equation is:

Let's take the first condition.  Let's say .  Then, substituting into our equation, we get:

, or

.

That is not sufficient to give us unique values for y and z.

The second condition, when transformed into math, tells us:

.

We can substitute this into the original equation, 

,

and get:

Which means that .

Then, we know that ,

or, 

.

But this also does not give us unique values for x and y.

But if we use BOTH of the statements, we know that z= 10 inches from the second statement, and x= 8 from the first statement, so we can solve for the last remaining rope length, and find that y=6.

Both of the statements together are necessary to solve the problem.

Example Question #3125 : Gmat Quantitative Reasoning

If  and  are integers, is  an even integer?

(1) 

(2) 

Possible Answers:

Both statements TOGETHER are not sufficient.

Each statement ALONE is sufficient.

Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient.

Both statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient

Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient.

Correct answer:

Both statements TOGETHER are not sufficient.

Explanation:

Using Statement (1):

 

In order to determine that 10-n is even, we need to know whether n is even or odd. If n is even, we can write:

In that case, m-n will be even. If n is odd, m-n will be odd as well.

Therefore, Statement (1) does not provide sufficient information to determine whether m-n is even.

Using Statement (2):

Although m>n, m and n could be even or odd integers. If m and n are both even, m-n will be even. If m and n are both odd, then m-n will be even. However, if either m or n is an even integer and the other is an odd integer, then m-n will be odd.

Statement (2) also does not provide enough information to determine whether m-n is even.

Therefore, Both statements TOGETHER are not SUFFICIENT.

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