GMAT Math : GMAT Quantitative Reasoning

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #1013 : Data Sufficiency Questions

You are given two positive integers,  and . Is their product divisible by 7?

Statement 1:  is divisible by 7.

Statement 2:  is divisible by 7.

Possible Answers:

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.

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.

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:

If we only know that  is divisible by 7, then  may or may not be a multiple of 7. 

Example 1: If , then , which is not divisible by 7.

Example 2: If , then , which is divisible by 7.

A similar argument shows that if we only know that   is divisible by 7, then  may or may not be a multiple of 7. 

 

Suppose we know both. 

If we know that  is divisible by 7, then, when  is divided by 7, the remainder is 1, and we can write for some integer :

If we know that  is divisible by 7, then, when  is divided by 7, the remainder is 6, and we can write for some integer :

Then 

  for some integer quotient 

So, when  is divided by 7, the remainder is 6, and  is not a multiple of 7. This makes the two statements together sufficient information.

Example Question #3131 : Gmat Quantitative Reasoning

You are given four numbers, .  You know that exactly one of these numbers has value 0. Which one is it?

Statement 1: 

Statement 2: 

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.

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.

Correct answer:

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

Explanation:

The product of two or more numbers is 0 if and only if at least one of the numbers is 0.

Each of the individual statements eliminates only two possible answers to the question; Statement 1 eliminates  and , and Statement 2 eliminates  and . The two together, however, eliminate all possible answers except for , leaving that to be the number worth zero.

Example Question #3132 : Gmat Quantitative Reasoning

I am thinking of two distinct prime numbers: what are they?

Statement 1: Both numbers are between 40 and 50.

Statement 2: Their difference is 2.

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.

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:

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

Explanation:

Statement 1 is not sufficient, since there are three primes - 41, 43 and 47 - between 40 and 50.

Statement 2 is not sufficient, since there are numerous pairs of primes that differ by 2 - 3 and 5 are one pair, as are 5 and 7.

Both statements together are sufficient, however; from Statement 1, we know that the primes are chosen from 41, 43, and 47, and from Statement 2, we know that we can only choose 41 and 43.

Example Question #3133 : Gmat Quantitative Reasoning

What is the last digit of whole number ?

Statement 1: The last digit of its base 5 representation is 2.

Statement 1: The last digit of its base 2 representation is 1.

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.

EITHER statement ALONE is 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:

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

Explanation:

If the base 5 representation of  ends in 2, then the division of the number by 5 results in a remainder of 2. Since every multiple of 5 ends in 0 or 5, this means that  ends in 2 or 7.

If the base 2 representation of  ends in 1, then the division of the number by 2 results in a remainder of 1. This makes  an odd number, which must end in 1, 3, 5, 7, or 9.

Neither statement alone provides a definitive answer to the question, but both facts taken together do - only a number ending in 7 satisfies both conditions.

Example Question #3134 : Gmat Quantitative Reasoning

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

Statement 1: Both are between 30 and 40.

Statement 2: Their product is 1,147.

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.

EITHER 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:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

There are only two prime numbers between 30 and 40 - they are 31 and 37. Statement 1 provides enough information.

There is only one way to factor 1,147 as the product of two primes:  . Statement 2 is also a giveaway.

Example Question #3135 : Gmat Quantitative Reasoning

A whole number has four digits. True or false: The integer is divisible by 9.

Statement 1: The sum of the digits is 26.

Statement 2: The last two digits are 98.

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. 

Statement 2 ALONE is sufficient to answer the question, but Statement 1 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.

EITHER statement ALONE is 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:

A necessary and sufficient condition for a whole number to be divisible by 9 is that the sum of its digits must be divisible by 9. Statement 1 provides proof that this condition is not met, since 26 is not a multiple of 9. Statement 2 provides irrelevant information.

Example Question #41 : Arithmetic

A whole number has four digits. True or false: The integer is divisible by 12.

Statement 1: The sum of the digits in the number is 36.

Statement 2: The last digit of the number is 9.

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 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.

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

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone. If the sum of the digits of a four-digit number is 36, then the average value of each digit is ; the only possible number that can have this property is 9,999, which is not divisible by 12 since

.

Now assume Statement 2 alone. For a number to be divisible by 12, it must also be divisible by any factors of 12, including 2. This is only possible if the last digit is even, which it is not. Therefore, the number is not divisible by 12.

Example Question #41 : Arithmetic

A whole number has four digits. True or false: The integer is divisible by 11.

Statement 1: The sum of the digits is 22.

Statement 2: The last two digits are 55.

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.

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.

EITHER statement ALONE is sufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are insufficient to answer the question.

Explanation:

Assume both statements to be true. The numbers 6,655 and 7,555 both end in 55 and have digit sum 22. However,

and

Only the former is divisible by 11, so the two statements together do not answer the question.

Example Question #43 : Arithmetic

True or false: Positive integer  is prime.

Statement 1: 

Statement 2: 

Possible Answers:

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.

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:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone. Then:

Either 

, in which case , or

, in which case 

Each of 5 and 7 has exactly two factors, 1 and itself, so either way  is prime.

Assume Statement 2 alone. Then:

Either

or 

Each of 7 and 11 has exactly two factors, 1 and itself, so either way  is prime.

Example Question #44 : Arithmetic

True or false: Positive integer  is prime.

Statement 1: The last digit of  is 4.

Statement 2: .

Possible Answers:

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 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.

Correct answer:

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

Explanation:

Assume Statement 1 alone. An integer is divisible by 2 if and only if its last digit is 0, 2, 4, 6, or 8. Therefore, it therefore follows that  is divisible by 2. Since the only prime number divisible by 2 is 2 itself, any integer ending in 4 must not be prime.

Assume Statement 2 alone. Then:

Either

, in which case  - a prime number, or 

, in which case  - a composite number since it has more than two factors (1, 2, 7, 14). 

Therefore, it is not clear whether or not  is prime.

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