GMAT Math : DSQ: Calculating the length of a side of a polygon

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #1 : Dsq: Calculating The Length Of A Side Of A Polygon

Thingy_4

Note: Figure NOT drawn to scale.

Refer to the above diagram. Evaluate .

Statement 1: 

Statement 2: 

Possible Answers:

xxx

Either alone

Correct answer:

Either alone

Explanation:

Refer to the figure below, in which  has been constructed, and the top and right sides of the figure have been extended to their intersection  to form Rectangle .

Thingy_4

Assume Statement 1 alone. Since opposite sides of a rectangle have the same length, . By segment addition, , and, since , by substitution, . Therefore, , and the Pythagorean Theorem can be used to find :

Since opposite sides of a rectangle have the same length, , and by segment addition, . By substitution, , and .

Assume Statement 2 alone. Since , the hypotenuse of right triangle , and , one of its legs, have lengths 15 and 12, respectively, the length of the other leg  can be found using the Pythagorean Theorem:

Example Question #2 : Dsq: Calculating The Length Of A Side Of A Polygon

Thingy

Note: Figure NOT drawn to scale

Refer to the above figure. Give the length of .

Statement 1: 

Statement 2: 

Possible Answers:

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.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER 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:

We can construct perpendicular line segments from  to  and from  to  as follows:

Thingy

 is the hypotenuse of a right triangle , so if we can determine the lengths of  and , we can use the Pythagorean Theorem to determine the length of .

Assume Statement 1 alone. By segment addition, .  Since  and  are opposite sides of a rectangle, ; similarly, . It follows by substitution that  . Since , it follows that , and . However, no additional information exists to find .

Assume Statement alone. By similar reasoning, ; since , and . However, no information exists to find .

The two statements put together, however, yield both necessary values:  and . By the Pythagorean Theorem,

.

Example Question #3 : Dsq: Calculating The Length Of A Side Of A Polygon

Thingy

Note: Figure NOT drawn to scale.

Refer to the above figure. What is the length of  ?

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.

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:

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

Explanation:

To find the length of , we can extend  to meet  at a point  to form two rectangles, as seen below:

Thingy

Statement 1 gives no helpful information, since the length of , which is not parallel to , has no bearing on that side's length.

If we are given Statement 2 alone, then, as seen in the diagram,  from segment addition, , from Statement 2, and from congruence of opposite sides of a rectangle,  and . Therefore, , and 

Example Question #4 : Dsq: Calculating The Length Of A Side Of A Polygon

Given a regular hexagon , what is the length of  ?

Statement 1: The hexagon is circumscribed by a circle with circumference .

Statement 2:  hs length 12.

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:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Below is a regular hexagon , with its three diameters, its center , and its circumscribed circle, which also has center .

Hexagon_2

If Statement 1 is true. then the circle, with circumference , has as its diameter , which is 12; this makes the two statements equivalent, so we need only establish that one statement is sufficient or insufficient.

Either way, , the radius of the hexagon, is 6. The six triangles that are formed by the sides and diameters of a regular hexagon are all equilateral by symmetry, so each side of the hexagon - in particular,  - has length 6.

Example Question #5 : Dsq: Calculating The Length Of A Side Of A Polygon

Give the length of side  of Hexagon

Statement 1: .

Statement 2: Hexagon  has perimeter 42.

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.

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.

EITHER statement ALONE is sufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are insufficient to answer the question.

Explanation:

Assume both statements to be true, and examine these two scenarios:

Case 1: The hexagon could have six sides of length 7.

Case 2: The hexagon has four sides of length 7, one of which is , one side of length 6, and one side -  - of length 8. 

In both situations,  and the perimeter of the hexagon is 42:

.

The conditions of both statements would be met in both scenarios, so the two statements together are insufficient.

Example Question #6 : Dsq: Calculating The Length Of A Side Of A Polygon

Give the length of side  of Pentagon 

Statement 1:

Statement 2:  and  both have length 10.

Possible Answers:

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.

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:

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

Explanation:

Statement 1 alone states that  is congruent to two other sides, but gives no actual measurements. Statement 2 alone gives the actual measurements of two other segments, but without further information, such as how their lengths relates to that of , no information about  can be inferred.

Now, assume both statements to be true. From Statement 2,  has length 10, and from Statement 2, , which is the same line segment (which can be named after its endpoints in either order), has the same length as . Therefore, .

Example Question #7 : Dsq: Calculating The Length Of A Side Of A Polygon

Give the length of side  of Pentagon 

Statement 1: Pentagon  has perimeter 50.

Statement 2: 

Possible Answers:

Statement 2 ALONE gives sufficient information to answer the question, but Statement 2 ALONE does NOT sufficient information to answer the question.

BOTH statements TOGETHER do not give sufficient information to answer the question.

EITHER statement ALONE gives sufficient information to answer the question.

Statement 1 ALONE gives sufficient information to answer the question, but Statement 2 ALONE does NOT sufficient information to answer the question.

BOTH statements TOGETHER give sufficient information to answer the question, but neither statement ALONE gives sufficient information to answer the question.

Correct answer:

Statement 2 ALONE gives sufficient information to answer the question, but Statement 2 ALONE does NOT sufficient information to answer the question.

Explanation:

Statement 1 alone only gives the perimeter - the sum of the lengths of the sides - but gives no information about the individual sidelengths. (In particular, there is no indication that the pentagon is regular).

Assume Statement 2 alone.  and  are two names for the same line segment, which can be named after its endpoints in either order. Therefore, .

Example Question #8 : Dsq: Calculating The Length Of A Side Of A Polygon

True or false:  is the shortest side of Pentagon .

Statement 1: Pentagon  has perimeter 65.

Statement 2: .

Possible Answers:

Statement 2 ALONE provides sufficient information to answer the question, but Statement 1 ALONE does NOT provide sufficient information to answer the question.

BOTH statements TOGETHER provide sufficient information to answer the question, but NEITHER statement ALONE provides sufficient information to answer the question.

Statement 1 ALONE provides sufficient information to answer the question, but Statement 2 ALONE does NOT provide sufficient information to answer the question.

EITHER Statement ALONE provides sufficient information to answer the question.

BOTH statements TOGETHER provide insufficient information to answer the question.

Correct answer:

BOTH statements TOGETHER provide insufficient information to answer the question.

Explanation:

Assume both statements are true. If the pentagon has sides of length 12, 13, 13, 13, and 14, with  the side of length 12, then  is the shortest side, and the perimeter is 

.

On the other hand, if the pentagon has sides of length 11, 12, 13, 14, and 15, 

with  the side of length 12, then  is not the shortest side, and the perimeter is 

.

The two statements together are insufficient.

Example Question #9 : Dsq: Calculating The Length Of A Side Of A Polygon

True or false:  is the longest side of Hexagon .

Statement 1: 

Statement 2:  Hexagon  has perimeter 66.

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:

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

Explanation:

Statement 1 alone only gives information about one side of the hexagon, and Statement 2 gives only information about the perimeter without giving any clues as to the individual sidelengths; neither is sufficient to answer the question.

Assume both statements are true. If , with length 10, is the longest side of Hexagon , then 

By the addition property of inequality, 

This means the sum of the sidelengths of the hexagon, which is its perimeter, is less than 66, in contradiction to Statement 2.  cannot be the longest side.

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