GMAT Math : Arithmetic

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #82 : Dsq: Calculating Discrete Probability

Some balls are placed in a large box; the balls include one ball marked "10", two balls marked "9", and so forth up to ten balls marked "1". A ball is drawn at random.

 is an integer between 1 and 10 inclusive. True or false: the probability that the ball will have the number  marked on it is greater than .

Statement 1:  is a prime integer.

Statement 2: 

Possible Answers:

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

EITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

Correct answer:

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

Explanation:

The total number of balls in the box will be 

.

Since 

,

it follows that the number of balls is

 .

The frequencies out of 55 of each outcome from 1 to 10, in order, are as follows:

Their respective probabilities are their frequencies divided by 55:

.

The probability that the ball will be marked "5" is 

;

therefore, the probability that the ball will be marked with any given integer less than or equal to 5 will be greater than 

The probability that the ball will be marked "6" is

 ;

therefore, the probability that the ball will be marked with any given integer greater than or equal to 6 will be less than 

Therefore, it suffices to know whether the number on the ball is less than or equal to 5. Statement 2 states that the number on the ball is less than or equal to 5, so it is sufficient to answer the question in the affirmative. Statement 1 is insufficient, since there are primes less than or equal to 5 - 2, 3, and 5 - and one prime greater than 5, which is 7.

Example Question #83 : Dsq: Calculating Discrete Probability

Some balls are placed in a large box; the balls include one ball marked "10", two balls marked "9", and so forth up to ten balls marked "1". A ball is drawn at random.

 is an integer between 1 and 10 inclusive. True or false: the probability that the ball will have the number  marked on it is greater than .

Statement 1:  is a perfect square integer.

Statement 2:  

Possible Answers:

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

EITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

Correct answer:

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

Explanation:

The total number of balls in the box will be 

.

Since 

,

it follows that the number of balls is

 .

The frequencies out of 55 of each outcome from 1 to 10, in order, is as follows:

Their respective probabilities are their frequencies divided by 55:

.

The probability that the ball will be marked "5" is 

;

therefore, the probability that the ball will be marked with any given integer less than or equal to 5 will be greater than 

The probability that the ball will be marked "6" is

 ;

therefore, the probability that the ball will be marked with any given integer greater than or equal to 6 will be less than 

Therefore, it suffices to know whether the number on the ball is less than or equal to 5.

Statement 1 alone is insufficient, since there are two perfect square integers from 1 to 5 (1 and 4) and one perfect square integer from 6 to 10 (9). Statement 2 alone is insufficient, since it is not clear whether the number on the ball is 5 or a number greater than 5. However, from the two statements together, it can be inferred that , and that the probability of drawing a ball with this number is .

Example Question #3221 : Gmat Quantitative Reasoning

A bag contains x red marbles, y blue marbles, and z green marbles.  What is the probability of drawing a green marble?

(1) There's a  probability of drawing a red marble.

(2) There's a  probability of drawing a blue marble.

Possible Answers:

EACH statement ALONE is sufficient.

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

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

Statements (1) and (2) TOGETHER are NOT sufficient.

BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient. 

Correct answer:

BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient. 

Explanation:

Probability is a part to whole comparison.  

With statement 1, we don't know nor can we determine the probability of drawing a green marble because we know nothing about the probability of drawing a blue marble. Therefore, statement 1 is not sufficient.

With statement 2, we don't know nor can we determine anything regarding the probability of drawing a red marble. Therefore, statement 2 is not sufficient.

However, taken together, we can determine that the probability of drawing a green marble is . Therefore, BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient. 

Example Question #3222 : Gmat Quantitative Reasoning

A coin is tossed n times. What is the probability of getting at least one tail?

(1) The probability of never flipping a head is .

(2) The probability of flipping at least one head is  .

Possible Answers:

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

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

Statements (1) and (2) TOGETHER are NOT sufficient.

BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

 EACH statement ALONE is sufficient.

Correct answer:

 EACH statement ALONE is sufficient.

Explanation:

Probability is the number of desired outcomes divided by the number of possible outcomes. 

With statement 1, we are told the probability of never flipping a head is , which is the same as always flipping a tail.  Since the probability of flipping a tail on a single flip is , we can determine the probability of flipping n tails is , which solves as  .  With n=3, we can solve for the probability of getting at least one tail is 1-probability of never getting a tail or 1-HHH:

.  

Therefore, statement 1 alone is sufficient.

With statement 2, we are told the probability of flipping at least one head is  . Since there are only 2 possible outcomes with each flip (heads or tails), the probability of flipping at least one head is the same as the probability of flipping at least one tail. Therefore, statement 2 alone is sufficient.

Therefore, the correct answer is EACH statement ALONE is sufficient.

Example Question #131 : Arithmetic

Oteri can choose to wear jeans, sweat pants, or shorts, a button down or a tee shirt, and a hat or no hat. How many different outfit combinations does he have in his wardrobe?

Possible Answers:

Correct answer:

Explanation:

He has 3 pants, 2 shirts, 2 hat choices (hat or no hat).

Example Question #132 : Arithmetic

Olivia picks  balls, each one after the other, from a basket containing  balls.

How many possible combinations of balls can she end up with?

(1) 

(2) 

Possible Answers:

Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient

Statements (1) and (2) TOGETHER are not sufficient

EACH statement ALONE is sufficient

Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient

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

Correct answer:

Statements (1) and (2) TOGETHER are not sufficient

Explanation:

Each statement on its own gives us one equation with 2 unknowns, which is unsolvable. Therefore each statement alone is not sufficient.

The two equations are equivalent: x + y = 13 and 2.(x+y) = 2 x 13 = 26

Therefore we cannot sole for x and y either with both equations.

Example Question #3 : Counting Methods

A Lunch Deal Meal at the Chinese restaurant where Jack likes to eat comprises one appetizer, one entree, and one beverage. How many possible Lunch Meal Deals can Jack choose from?

Statement 1: Jack can choose from seven appetizers and ten entrees.

Statement 2: Jack can choose from as many beverages as appetizers.

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.

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 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:

By the multiplication principle, the number of meals Jack can make is the product of the number of appetizers, the number of entrees, and the number of beverages. Statement 1 tells only the first two; Statement 2 does not give any of these quantities. From the two statements together, we know that there are seven appetizers, ten entrees, and seven beverages, so there are  possible Lunch Deal Meals.

Example Question #133 : Arithmetic

A Veggie Platter at the restaurant where Lucy likes to eat comprises four different vegetables. How many possible Veggie Platters can Lucy choose from?

Statement 1: The Veggie Platter costs $5.29 plus tax.

Statement 2: The menu from which Lucy may choose her vegetables is below:

Veggie_menu

 

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 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.

EITHER statement ALONE is 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:

Statement 1 alone gives irrelevant information; the cost of the Veggie Platter has no bearing on the number of possible combinations.

From Statement 2 alone, it can be determined that there are ten choices; therefore, the number of ways Lucy can order a Veggie Platter can be determined to be .

Example Question #4 : Counting Methods

A Veggie Platter at the restaurant where Georgia likes to eat comprises four different vegetables. How many possible Veggie Platters can Georgia choose from?

Statement 1: Half the choices are listed as being "hearth healthy".

Statement 2: Seven of the choices are not listed as being "hearth healthy".

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.

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.

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:

The only thing needed in order to answer the question is the number of vegetables from which Georgia has to choose. Neither statement alone gives this information.

However, it is possible to deduce this information from both statements together. From Statement 1, half the choices are "hearth healthy"; therefore, half are not. From Statement 2, this amounts to seven choices, so the total number of vegetables on the menu is fourteen, and there are a total of  possible Veggie Platters.

 

Example Question #133 : Arithmetic

A Veggie Platter at the restaurant where George likes to eat comprises four different vegetables. How many possible Veggie Platters can George choose from?

Statement 1: George can choose from ten vegetables.

Statement 2: The choices are black-eyed peas, corn on the cob, and mashed potatoes, among seven others.

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.

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.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Each statement alone says that George can choose from ten vegetables - Statement 2 is different only in that it names three of them. George can choose any one of  different Veggie Platters.

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