# GRE Subject Test: Math : Union & Intersect

## Example Questions

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### Example Question #1 : Real Analysis

What is ?

Possible Answers:

Correct answer:

Explanation:

means the intersection of set A and set C. Intersection means that you want to choose only the numbers that are in BOTH set A and set C. The only numbers that are in common to those two sets are 3 and 9.

### Example Question #9 : Real Analysis

What is ?

Possible Answers:

Correct answer:

Explanation:

means the union of set B and set C. Union means to include all the numbers that are in either set B or set C (without listing duplicates twice). The numbers 1, 3, 5, 8, 9, and 11 appear in B and the numbers 2, 3, 5, 6, 9, 12 appear in C. Including all of those numbers in the set symbol gives the correct answer.

### Example Question #1 : Real Analysis

Let universal set  be the set of all people. Let  represent Brittany.

Let  be the set of people who like James Blunt, , the set of people who like John Legend, and , the set of people who like Pharrell Williams.

True or false: Brittany likes James Blunt, John Legend, and Pharrell Williams.

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.

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.

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:

Assume Statement 1 alone.  is the intersection of the sets , and . Since Brittany falls in this intersection, she falls in all three sets, and it follows that she likes all three of James Blunt, John Legend, and Pharrell Williams.

Assume Statement 2 alone.  is the union of the three sets. Since Brittany falls in this union, she falls in one, two, or all three sets, which means that she likes at least one of James Blunt, John Legend, and Pharrell Williams. However, more information is needed before it can be established whether or not she likes all three.

### Example Question #1 : Relations

Let be the universal set of all people. Let be the set of all people who are dancers and be the set of all people that are singers.

Let represent Jeremy. Which of these statements states the opposite of  "Jeremy is not a dancer, but he is a singer" in set notation?

Possible Answers:

Correct answer:

Explanation:

In set notation, "Jeremy is not a dancer, but he is a singer" can be stated as

That is, Jeremy falls in the intersection of the complement of the set of dancers  and the set of singers .

The opposite of this is that is in the complement of this set:

By DeMorgan's law, this is equivalent to saying

, or

.

### Example Question #2 : Relations

Let  be the universal set of all people. Let  be the set of all people who like Band A. Let  be the set of all people who like Band B. Let  be the set of all people who like Band C. Let  stand for Julianna.

Let . Which of the following could be true?

Possible Answers:

Julianna likes Band B and Band C, but not Band A.

Julianna likes Band C, but not Band A or Band B.

Julianna likes Band A and Band B, but not Band C.

Julianna likes Band B, but not Band A or Band C.

Julianna likes Band A and Band C, but not Band B.

Correct answer:

Julianna likes Band A and Band C, but not Band B.

Explanation:

, which is the intersection of  and . It follows that  and .

, so it follows that Julianna likes Band A. The three choices that state that she does not can be eliminated.

. This is the union of , the complement of  - that is, the set of people not in  - and . It follows that either Julianna does not like Band B, does like Band C, or both. Therefore, it is not true that she likes Band B and does not like Band C. This can be eliminated.

The only possible choice is that Julianna likes Band A and Band C, but not Band B.

### Example Question #1 : Union & Intersect

What is the intersection of :

Set A={}
Set B={}

Possible Answers:

None of the Above

{}

{}

{}

Correct answer:

{}

Explanation:

Step 1: Recall the definition for intersection of two sets: The intersection of two sets is a subset that has numbers that is shared between two sets, A and B.

Step 2: Find the shared elements between both sets

Set A and Set B both share 4,11, and 14.

The intersection of both sets is {}

### Example Question #1 : Union & Intersect

What is the union of the following sets:

Set A={}
Set B={}

Possible Answers:

{}

{}

{}

None of the Above

Correct answer:

{}

Explanation:

Step 1: Define the union of two sets. The union of two sets is all elements that are in two sets, as well as the elements that are shared.

Step 2: Find the union of the sets:

Set A has elements:
Set B has elements:

Union of Set A and B () is {}

### Example Question #1 : Union & Intersect

What is the intersection of Set A:  and Set B:

Possible Answers:

There is no intersection

Correct answer:

There is no intersection

Explanation:

Step 1: Define what the intersection of two sets means.. The intersection of two sets is defined as a set that has elements that are shared between both original sets..

Step 2: Find any shared elements..

If we look, Set A and Set B do not share any elements..

Therefore, there is no intersection of the two sets.

### Example Question #1 : Union & Intersect

Evaluate

Possible Answers:

Correct answer:

Explanation:

This question asks you to find the intersection of the sets B and D. Include only the numbers that both sets have in common with one another. The only common number with both sets is 4.

### Example Question #1 : Union & Intersect

Evaluate

Possible Answers:

Correct answer:

Explanation:

Always start by doing the parentheses first. Do the union of C and B which means to include all the elements from both sets without including duplicates. The numbers do not need to be in any order. Sometimes it can help to put the elements from one entire set before putting the elements in the other

Now, take the results from C union B and do the intersection of those elements with set D. Intersection means to include the elements that are common to both sets.

The final answer is

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