GMAT Math : Geometry

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #2247 : Gmat Quantitative Reasoning

Lines_3

Note: Figure NOT drawn to scale.

Refer to the above figure. Evaluate .

Statement 1:  and  are complementary.

Statement 2: 

Possible Answers:

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.

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. 

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.  and  are vertical from  and , respectively, so  and  and  form a complementary pair, so, by definition 

and by substitution,

.

Assume Statement 2 alone. Since  is a right triangle whose hypotenuse is  times as long as a leg, it follows that  is a 45-45-90 triangle, so .

 , and  together form a straight angle, so their degree measures total 

But without further information, the sum of the degree measures of only  and  cannot be calculated.

Example Question #22 : Lines

Lines_3

Note: Figure NOT drawn to scale.

Refer to the above diagram. What is the measure of  ?

Statement 1:  is a  angle.

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 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.

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:

Statement 1 alone gives insufficient information to find the measure of .

, and  together form a angle; therefore,

, so by substitution,

But with no further information, the measure of  cannot be calculated.

Statement 2 alone gives insufficient information for a similar reason. , , and  together form a  angle; therefore,

Since , we can rewrite this statement as

Again, with no further information, the measure of  cannot be calculated.

Assume both statements to be true.   and  are a pair of vertical angles, so , and . Since , then . Also, 

By substitution,

 

Example Question #23 : Lines

Lines_4

Note: You may assume that  and  are not parallel lines, but you may not assume that  and  are parallel lines unless it is specifically stated.

Refer to the above diagram. Is the sum of the measures of  and  less than, equal to, or greater than ?

Statement 1: There exists a point  such that  lies on  and  lies on .

Statement 2: Quadrilateral  is not a trapezoid.

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. 

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:

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. Since  exists and includes ,   and  are one and the same—and this is . Similarly,  is . This means that  and  have a point of intersection, which is . Since  falls between  and  and  falls between  and , the lines intersect on the side of  that includes points  and . By Euclid's Fifth Postulate, the sum of the measures of  and  is less than .

Assume Statement 2 alone. Since it is given that , the other two sides,  and  are parallel if and only if Quadrilateral  is a trapezoid, which it is not. Therefore,   and  are not parallel, and the sum of the degree measures of same-side interior angles   and  is not equal to . However, without further information, it is impossible to determine whether the sum of the measures is less than or greater than .

Example Question #135 : Data Sufficiency Questions

Lines_3

Note: Figure NOT drawn to scale.

Refer to the above figure. Evaluate .

Statement 1: 

Statement 2: 

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 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 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.  and  are congruent legs of right triangle , so their acute angles, one of which is , measure  and  form a pair of vertical, and consequently, congruent, angles, so .

Statement 2 alone gives insufficient information, as  and  has no particular relationship that would lead to an arithmetic relationship between their angle measures.

Example Question #25 : Lines

Lines_3

Note: Figure NOT drawn to scale.

Refer to the above diagram. What is the measure of  ?

Statement 1:  is an equilateral triangle.

Statement 2: 

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.

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. 

Correct answer:

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

Explanation:

, and  together form a straight angle, so their measures total ; therefore,

Assume Statement 1 alone. The angles of an equilateral triangle all measure , so  and  form a pair of vertical angles, so they are congruent, and consequently, . Therefore,

But with no further information,  cannot be calculated.

Assume Statement 2 alone. It follows that 

Again, with no further information,  cannot be calculated.

Assume both statements to be true.  as a result of Statement 1, and  from Statement 2, so

Example Question #141 : Data Sufficiency Questions

Lines_3

Note: Figure NOT drawn to scale.

Refer to the above figure. Evaluate .

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 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.

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:

Assume Statement 1 alone. , and  together form a straight angle, so their degree measures total 

Without further information, no other angle measures, including that of , can be found.

Assume Statement 2 alone. , and  together form a straight angle, so their degree measures total 

Without further information, no other angle measures, including that of , can be found.

However, if both statements are assumed to be true, it follows from Statements 2 and 1 respectively, as seen before, that  and , so

.

Example Question #27 : Lines

Lines_3

Note: Figure NOT drawn to scale.

Refer to the above figure. Give the measure of .

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.

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.

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

Correct answer:

BOTH statements TOGETHER are insufficient to answer the question. 

Explanation:

Assume both statements to be true. We show that the two statements provide insufficient information by exploring two scenarios:

Case 1: 

 and  are vertical from  and , respectively, so  and , and 

 

Case 2: 

 

The conditions of both statements are met, but  assumes a different value in each scenario.

Example Question #28 : Lines

Lines_3

Note: Figure NOT drawn to scale.

Refer to the above diagram. Evaluate .

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.

EITHER 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:

Assume Statement 1 alone.  , and  together form a straight angle, so their measures total ; therefore,

However, without any further information, we cannot determine the sum of the measures of  and .

Assume Statement 2 alone.  , and  together form a straight angle, so their measures total ; therefore,

Again, without any further information, we cannot determine the sum of the measures of  and .

Assume both statements are true. Since the measures of  and  can be calculated from Statements 1 and 2, respectively. We can add them:

Example Question #29 : Lines

Lines_3

Note: Figure NOT drawn to scale.

Refer to the above diagram. Evaluate .

Statement 1: 

Statement 2:  is an equilateral triangle.

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.

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. 

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone.  and  are a pair of vertical angles, as are  and . Therefore, 

 

By substitution,

.

Assume Statement 2 alone. The angles of an equilateral triangle all measure , so .

,  , and  together form a straight angle, so , 

Example Question #1 : Dsq: Understanding Intersecting Lines

Lines

Refer to the above figure. Jane chose one of the line segments shown in the above diagram but she will not reveal which one. Which one did she choose?

Statement 1: One of the endpoints of the line segment is .

Statement 2: The line segment includes .

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.

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.

Correct answer:

BOTH statements TOGETHER are insufficient to answer the question.

Explanation:

If we know both statements, then we know that the segment can be either  or , since each has endpoint  and each includes ; we can not eliminate either, however.

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