GMAT Math : Geometry

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #1 : Dsq: Understanding Rays

, and  are distinct points.

True or false:  and  are the same ray.

Statement 1: .

Statement 2:  is the midpoint of .

Possible Answers:

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 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. 

Correct answer:

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

Explanation:

We show Statement 1 alone is insufficient to determine whether the two rays are the same by looking at the figures below:

Rays

In both figures, , but only in the first figure,  and  are the same ray.

Assume Statement 2 alone. If  is the midpoint of ,  must be on , as in the top figure, so  and  are one and the same.

Example Question #2 : Dsq: Understanding Rays

, and  are distinct points.

True or false:  and  are the same ray.

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 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.

Correct answer:

BOTH statements TOGETHER are insufficient to answer the question. 

Explanation:

We show that both statements together provide insufficient information by giving two scenarios in which both statements are true.

Case 1: , and  are noncollinear. The three points are vertices of a triangle, and by the Triangle Inequality Theorem, 

 and

.

Also, since the three points are not on a single line,  and  are parts of different lines and cannot be the same ray.

Case 2:   with length 2 and midpoint .

Rays

 and , so ; similarly, . Also,  and  are the same ray, since they have the same endpoint and  is on .

Example Question #3 : Dsq: Understanding Rays

, and  are distinct points.

True or false:  and  are the same ray.

Statement 1: , and  are collinear.

Statement 2: .

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 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.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER 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 does not prove the rays to be the same or different, as seen in these diagrams:

Rays

In both figures, , and  are collinear, satisfying the condition of Statement 1. But In the top figure,  and  are the same ray, since  is on ; in the bottom figure, since  is not on  and  are distinct rays.

Assume Statement 2 alone. Suppose  and  are not the same ray. Then one of two things happens:

Case 1: , and  are noncollinear. The three points are vertices of a triangle, and by the triangle inequality, 

,

contradicting Statement 2.

Case 2: , and  are collinear.  must be between  and , as in the bottom figure, since if it were not,  and  would be the same ray. By segment addition, 

,

contradicting Statement 2.

By contradiction,  and  are the same ray.

Example Question #11 : Geometry

What is the measure of ?

Statement 1:  is complementary to an angle that measures .

Statement 2:  is adjacent to an angle that measures .

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 insufficient 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.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 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:

Complementary angles have degree measures that total , so the measure of an angle complementary to a  angle would have measure . If Statement 1 is assumed, then .

Statement 2 gives no useful information. Adjacent angles do not have any numerical relationship; they simply share a ray and a vertex.

Example Question #12 : Geometry

Lines

Note: Figure NOT drawn to scale.

Refer to the above diagram.

What is 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.

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.

Correct answer:

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

Explanation:

If we only know that , then we cannot surmise anything from the diagram about the measure of . But  and  are vertical angles, which must be congruent, so if we know , then  also.

Example Question #13 : Geometry

 and  are supplementary angles. Which one has the greater measure?

Statement 1:  

Statement 2:  is an obtuse angle.

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

Explanation:

By definition, if  and  are supplementary angles, then .

If Statement 1 is assumed and , then . This does not answer our question, since, for example, it is possible that  and , or vice versa.

If Statement 2 is assumed, then , and subsequently, ; by transitivity, .

Example Question #14 : Geometry

Lines_3

Note: Figure NOT drawn to scale.

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

Statement 1: 

Statement 2:  is a  angle.

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.

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. 

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone. Since  and  form a linear pair, their measures total . Therefore, this fact, along with Statement 1, form a system of linear equations, which can be solved as follows:

The second equation can be rewritten as 

and a substitution can be made:

Assume Statement 2 alone.  and  are a pair of vertical angles, which have the same measure, so  .

Example Question #15 : Geometry

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: 

Statement 2: 

Possible Answers:

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.

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.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone.  and  form a linear pair of angles, so their measures total ; the same holds for  and . Therefore,

Assume Statement 2 alone.  and  form a linear pair of angles, so their measures total ; the same holds for  and . Therefore,

, , and  are the four angles of Quadrilateral , so their degree measures total 360. Therefore,

Example Question #6 : Dsq: Calculating An Angle Of A Line

Find the angle made by  and the -axis.

I)  goes through the origin and the point .

II)  makes a  degree angle between itself and the -axis.

Possible Answers:

Both statements are needed to answer the question.

Statement II is sufficient to answer the question, but statement I is not sufficient to answer the question.

Either statement is sufficient to answer the question.

Neither statement is sufficient to answer the question. More information is needed.

Statement I is sufficient to answer the question, but statement II is not sufficient to answer the question.

Correct answer:

Either statement is sufficient to answer the question.

Explanation:

To find the angle of the line, recall that each quadrant has 90 degrees

I) Tells us that the line has a slope of one. This means that if we make a triangle using our line, the x-axis and a line coming up from the x-axis at 90 degrees we will have a 45/45/90 triangle. Therefore, I) tells us that our angle is 45 degrees.

II) Tells us that the line makes a 45 degree angle between itself and the y-axis. Therefore:

Therfore, we could use either statement.

Example Question #16 : Geometry

Lines_3

Note: Figure NOT drawn to scale.

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

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.

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. 

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.

Correct answer:

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

Explanation:

Assume Statement 1 alone.  and  are a pair of vertical angles and are therefore congruent, so the statement

can be rewritten as

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

But without further information, the measure of  cannot be calculated.

Assume Statement 2 alone.  and  are a pair of vertical angles and are therefore congruent, so the statement

can be rewritten as

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