# GRE Subject Test: Math : Union & Intersect

## Example Questions

### Example Question #1 : Union & Intersect

What is ?

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 #2 : Union & Intersect

What is ?

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 #11 : Word Problems

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:

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.

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.

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 : Union & Intersect

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?

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 #1 : Union & Intersect

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?

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

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

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

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

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

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 : Relations

What is the intersection of :

Set A={}
Set B={}

{}

{}

{}

None of the Above

{}

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={}

{}

{}

{}

None of the Above

{}

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 #131 : Other Topics

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

There is no intersection

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

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.

Evaluate