GMAT Math : GMAT Quantitative Reasoning

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #181 : Gmat Quantitative Reasoning

Read the following problem:

A scientist needs one liter of 20% hydrochloric acid solution; however, he only has two one-liter bottles of solution on hand, one of which is 15% acid and one of which is 35% acid. How much of each solution must he mix together to get the solution he wants?

Let  be the number of milliliters of 15% solution he will use and  be the number of milliliters of 35% solution he will use. Which of the following systems of equations will yield the correct values of both?

Possible Answers:

Correct answer:

Explanation:

Since  and  are being set to numbers of milliliters, we convert one liter to 1,000 milliliters. The sum of the amounts of the two solutions  and  is 1,000, so

is one equation of the system.

The other equation will add the acid. The amount of acid in an acid solution is the concentration, as a decimal, multiplied by the amount of solution. The amount of acid in the pre-mixture solutions are  and ; add these to get the amount of acid in 1,000 milliliters of a 20% solution, or  milliliters:

 

The correct system is:

Example Question #182 : Word Problems

Pieces of Rainbow Candy come in six colors, including green; the machines are carefully set to make sure each batch of sixty pounds contains an equal amount of candy of each color.

One day, something went wrong, and one sixty-pound batch only contained half as much green candy as it was supposed to; the other five colors were distributed equally. How many pounds of green candies needed to be added to this batch in order to restore the correct distribution of colors?

Possible Answers:

Correct answer:

Explanation:

Since a normal batch of candies is one-sixth green candies, then it contains  pounds of green candies; the defective batch contained half this, or 5 pounds. If we let  be the number of pounds of green candies that were added, then, after the addition, there were  pounds of green candies in a batch of  candies. One sixth of the candies are green, so set and solve the equation:

Six pounds of green candies are added.

 

Example Question #183 : Word Problems

Pieces of Rainbow Candy come in six colors, including white; the machines are carefully set to make sure each batch of forty-eight pounds contains an equal number of each color candy.

One day, something went wrong, and one forty-eight-pound batch only contained half as much white candy as it was supposed to; the other five colors were distributed equally. White candies were added to this batch until the correct color distribution was restored. To the nearest pound, how many pounds of candy ended up in this corrected batch?

Possible Answers:

Correct answer:

Explanation:

Initially, there were 48 pounds of candies. In a normal batch, one sixth of them, or  pounds, should be white, but in the defective batch, half this, or 4 pounds, were white. Subsequently, 44 pounds of candies in the defective batch were not white.

Let  be the number of pounds of candy in the batch after the white candies were added. Since  of a normal batch of candies are not white,  pounds of candies are not white; since no candies that weren't white were added, 

The closest choice, and the correct one, is 53 pounds.

Example Question #21 : Mixture Problems

Before being slightly dried, an apple is made of  of water. After the apple is slightly dried, the water accounts only for  of the weight of the fruit. Originally, the apple weighed . What is its weight after being dried? Consider the difference in weight to be solely caused by the evaporating water.

Possible Answers:

Correct answer:

Explanation:

First, we should find out what isn't water in the apple; let's call this the pulp. The pulp accounts for  of the weight of the fruit before being dried. Therefore, the pulp weighs . We can then express as a ratio the amount of pulp in the apple to the total weight of the fruit after it has been slightly dried as follows: 

We can rearrange this equation to yield: 

The weight of the water in the dried fruit is therefore . To this weight we simply add the weight of the pulp and we get the final answer, 

Example Question #185 : Word Problems

Two jars of equal size each contain some saltwater solution. The first jar is 20% full of a solution which is 80% salt; the second jar is 80% full of a solution which is 20% salt. The contents of the jars are mixed. What is the concentration of salt in the combined solution?

Possible Answers:

Correct answer:

Explanation:

For the sake of simplicity, assume that each jar holds 100 milliliters of water - this reasoning is independent of the actual capacity. 

The first jar is 20% full, so it contains  milliliters of solution; this solution is 80% salt, so there are  millilters of salt in the solution. Similarly, the second jar includes  milliliters of solution, which include  milliliters of salt.

Therefore, when the two solutions are mixed, the concentration of salt will be

.

Example Question #181 : Word Problems

Two jars of equal capacity each contain a saltwater solution. The first jar is 40% full, and its solution is 60% salt. If the contents of the second jar are emptied into the first jar, the solution, which will fill the jar completely, will be 30% salt. 

What is the salt concentration of the contents of the second jar?

Possible Answers:

Correct answer:

Explanation:

For the sake of simplicity, let us assume that each jar has capacity 100 milliliters; the reasoning is the same regardless of the common capacity. 

The first jar is 40% full, so there are  milliliters of solution in the jar; the solution is 60% salt, so there are  milliliters of salt in the solution. 

For the first jar to be filled to capacity,  milliliters of solution must be added. Also, if the solution is 30% salt, then the jar will contain milliliters of salt. This means that  milliliters of salt will have been added. This means that the concentration of salt in the added solution - the contents of the second jar - is

.

(Note that the actual size of the second jar does not matter.)

 

Example Question #181 : Problem Solving Questions

Charlie, the barrista at Sunday Coffee, has a problem. He must mix together Licorice Dream tea, which costs $20/lb, and Strawberry Explosion tea, which costs $12/lb to make sixty pounds of a new flavor of tea. Unfortunately, he forgot the correct proportions. He does know that the new tea costs $14/lb.

How many pounds of the Licorice Dream tea go into the mix? 

(You may assume that the tea is to sell for the same amount of money as if it had been sold separately.)

Possible Answers:

None of the other answers are correct

Correct answer:

None of the other answers are correct

Explanation:

Let  be the number of pounds of Licorice Dream tea; then  is the number of pounds of Strawberry Explosion. Then the total value of each ingredient tea, as well as the total value of the new tea, will be:

Licorice:  or 

Strawberry:  or 

New tea: 

 

Add the individual costs of the ingredient teas to get the total cost of the new tea.

Charlie will use 15 pounds of the Licorice Dream; as this is not one of the given answers, the correct answer is "None of the answers are correct".

Example Question #1 : Data Interpretation

Two dice are rolled. What is the probability that the sum of both dice is greater than 8?

Possible Answers:

\small \frac{5}{18}

\small \frac{5}{9}

\small \frac{1}{8}

\small \frac{7}{18}

Correct answer:

\small \frac{5}{18}

Explanation:

There are 36 possible outcomes (). 10 out of the 36 outcomes are greater than 8: (6 and 3)(6 and 4)(6 and 5)(6 and 6)(5 and 4)(5 and 5)(5 and 6)(4 and 5)(4 and 6)(3 and 6).

\small \frac{10}{36}\ =\ \frac{5}{18}

Example Question #1 : Calculating Probability

Among a group of 300 people, 15% play soccer, 21% play baseball, and 9% play both soccer and baseball. If one person is randomly selected, what is the probability that the person selected will be one who plays baseball but NOT soccer?

Possible Answers:

Correct answer:

Explanation:

Since there are 300 people,  people play baseball and  of those people play both baseball and soccer. Therefore, there are  people who play baseball but not soccer.

Probability:

Example Question #3 : Data Interpretation

If a die is rolled twice, what is the probability that it will land on either 2 or an odd number both times?

Possible Answers:

Correct answer:

Explanation:

probability on one roll:

for both times=

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