GMAT Math : DSQ: Calculating the midpoint of a line segment

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #1 : Dsq: Calculating The Midpoint Of A Line Segment

A line segment has one of its endpoints at . In which quadrant, or on what axis, is its other endpoint?

Statement 1: The midpoint of the segment is .

Statement 2: The length of the segment is 10.

Possible Answers:

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.

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.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Statement 1 give us the means to find the other endpoint using the midpoint formula:

Similarly, 

This makes the endpoint , which is in Quadrant I.

 

Statement 2 is also sufficient. , which is in Quadrant 1, is 12 units away from the nearest axis; since the length of the segment is 10, the entire segment must be in Quadrant I.

 

Example Question #2 : Dsq: Calculating The Midpoint Of A Line Segment

In what quadrant or axis is the midpoint of the line segment with endpoints  and  located?

Statement 1: 

Statement 2:  is in Quadrant IV.

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 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.

BOTH statements TOGETHER are insufficient 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:

The midpoint of the segment with endpoints  and  is .

If , then  and , so the midpoint, having both of its coordinates positive, is in Quadrant I.

 

If  is in Quadrant IV, then  and . But the quadrant of the midpoint varies according to  and :

 

Example 1: If , the midpoint is , or , putting it in Quadrant I. 

Example 2: If , the midpoint is , or , putting it in Quadrant III. 

 

Therefore, the first statement, but not the second, tells us all we need to know.

Example Question #3 : Dsq: Calculating The Midpoint Of A Line Segment

Consider segment . What are the coordinates of the midpoint of ?

I) Point  has coordinates of .

II) Point  has coordinates of .

 

Possible Answers:

Both statements taken together are sufficient to solve the question.

Statement 2 is sufficient to solve the question, but statement 1 is not sufficient to solve the question.

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

Statement 1 is sufficient to solve the question, but statement 2 is not sufficient to solve the question.

Each statement alone is enough to solve the question.

Correct answer:

Both statements taken together are sufficient to solve the question.

Explanation:

We are asked to find the midpoint of a line segment and given endpoints in our clues.

Midpoint formula is found by taking the average of the x and y values of two points.

We need both endpoints to solve this problem, so both statements are needed. 

Example Question #4 : Dsq: Calculating The Midpoint Of A Line Segment

Find the midpoint of segment  given that point  is at .

I) The  coordinate of  is twice that of , and the  coordinate of  is  that of .

II)  is  units long.

 

Possible Answers:

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

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

Both statements together are needed to answer the question.

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

Either statement alone is sufficient to answer the question.

Correct answer:

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

Explanation:

To find the midpoint, we need to know both endpoints.

I) Gives us the means to find out other endpoint.

II) Gives us the length of PS, but we are not given any hint as to its orientation.Thus, we cannot find the other endpoint and we cannot find the midpoint.

Thus, Statement I alone is sufficient to answer the question.

Example Question #5 : Dsq: Calculating The Midpoint Of A Line Segment

Find the midpoint of segment .

I) Endpoint  has coordinates of .

II) Endpoint   coordinate is half of , and   coordinate is one sixteenth of   coordinate.

Possible Answers:

Either statement is sufficient to answer the question.

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

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

Both statements are needed to answer the question.

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

Correct answer:

Both statements are needed to answer the question.

Explanation:

To find the midpoint of a segment we need both endpoints

I) Gives us one endpoint.

II) Gives us clues to find the other endpoint. 

 has coordinates of 

Use midpoint formula

 

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