GMAT Math : Other Quadrilaterals

Study concepts, example questions & explanations for GMAT Math

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Example Questions

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Example Question #21 : Quadrilaterals

Parallelogram

NOTE: Figure NOT drawn to scale.

Is the above figure a parallelogram?

Statement 1: 

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.

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:

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

Explanation:

Knowing one pair of sides of a quadrilateral to be congruent is not alone sufficient to prove that figure to be a parallelogram, nor is knowing one pair of sides of a quadrilateral to be parallel. But knowing both about the same pair of sides is sufficient by a theorem of parallelograms.

Example Question #2 : Other Quadrilaterals

Trapezoid

Notes:  refers to the length of the entire dashed line. Figure not drawn to scale.

 

Calculate , the height of the large trapezoid.

Statement 1: 

Statement 2: The area of the trapezoid is 7,000.

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.

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.

Correct answer:

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

Explanation:

Consider the area formula for a trapezoid:

 is the midsegment of the trapezoid, which, by the Trapezoid Midsegment Theorem, has length equal to the mean of the bases - in other words, . The area formula can be expressed, after substitution, as 

So, if you know both the area and  - but not just one - you can find the height by dividing.

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

Consider parallelogram .

I) The perimeter of  is  light years.

II) Side  is  light years and is equivalent to side .

Find the length of side .

Possible Answers:

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.

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.

Both statements are needed to answer the question.

Correct answer:

Both statements are needed to answer the question.

Explanation:

We can work backwards from the perimeter to find the length of the unknown side.

I) Gives us the perimeter.

II) Gives us two of the sides.

In a parallelogram there are two sets of corresponding sides. We can use I) and II) to write the following equaiton, where l is the length of our wanted side.

Solve for l to find our final side:

Example Question #4 : Other Quadrilaterals

Calculate the side of a square.

Statement 1:  A circle with an area of  is enclosed inside the square and touches all four edges of the square.

Statement 2:  A circle with a circumference of  encloses the square and touches all four corners of the square.

Possible Answers:

Correct answer:

Explanation:

Statement 1:  A circle with an area of  is enclosed inside the square and touches all four edges of the square.

Write the formula for the area of the circle.

 

After substituting the value of the area and solve for radius, the radius is 1.  The side length of the square is double the length of the radius.

Statement 2:  A circle with a circumference of  encloses the square and touches all four corners of the square.

Write the formula for the circumference of the circle.

After substituting the value of the circumference and solve for diameter, the diameter of the circle is 1.  This diameter represents the diagonal of the square.  Because the square length and width are equal dimensions, it is possible to solve for the lengths of the square by Pythagorean Theorem knowing just the length of the square diagonal.

Therefore:

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

Consider isosceles trapezoid .

I)  has a perimeter of .

II) The larger base of  is 45 times bigger than the smaller base.

Find the length of the two legs of .

Possible Answers:

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.

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.

Both statements are needed to answer the question.

Correct answer:

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

Explanation:

Consider isosceles trapezoid .

I)  has a perimeter of .

II) The larger base of  is 45 times bigger than the smaller base.

Find the length of the two legs of .

 

To find the length of the legs of a trapezoid, we need the perimeter and the two bases. Then, we can subtract the sum of the two bases from the perimeter and divide by two to find the lengths of the sides we are looking for.

Statement I gives us the perimeter of .

Statement II relates the two bases of .

We are told that  is an isosceles trapezoid, which means its two legs are equal; however, we still have too many unknowns and not enough equations. There is no way to solve this without more information.

We still have three unknowns and two equations, so we cannot solve this system of equations.

Example Question #1 : Dsq: Calculating The Perimeter Of A Quadrilateral

What is the perimeter of Rhombus  ?

Statement 1:  has perimeter .

Statement 2:  is equilateral.

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.

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:

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

Explanation:

Each diagonal divides Rhombus  into two triangles, both isosceles.

Statement 1 alone establishes the perimeter of one such triangle. However, it does not make it clear what equal side lengths  and  and diagonal length  are. For example,  fits the perimeter, but so does .

Statement 2 alone gives no information about the actual lengths of the sides.

Assume both statements are true. Since  is equilateral, . It follows that , and . Also, the diagonals of a rhombus bisect their angles and are each other's perpendicular bisectors, so the rhombus, with their diagonals, is given below.

Rhombus

 has perimeter , which means that 

Since  is known to be a  triangle, the proportions of the side lengths are known; along with the above equation, , and, subsequently, the perimeter, can be determined.

Example Question #1 : Dsq: Calculating The Perimeter Of A Quadrilateral

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What is the perimeter of quadrilateral

(1) Diagonal  and are perpendicular with midpoint .

(2) 

Possible Answers:

Statement 2 alone is sufficient

Both statements together are sufficient

Each statement alone is sufficient

Statements 1 and 2 together are not sufficient

Statement 1 alone is sufficient

Correct answer:

Both statements together are sufficient

Explanation:

To find the perimeter of the quadrilateral, we need to know whether it is of a special type of quadrilaterals and we need to know the length of the sides.

Statement 1 tells us only that the quadrilateral is a rhombus. Indeed, a quadrilateral with perpendicular diagonals intersecting at their midpoint must be a rhombus. However we don't know any length of the sides. 

Statement 2 says gives us the length us two consecutive sides. It could be tempting to answer that it is sufficient, however, we can't conclude that the quadrilateral has equal lengths. Therefore this statement alone is insufficient.

 

Both statements together are sufficient since we can conclude that the quadrilateral is a rhombus, and twice   will give us the perimeter.

Example Question #2 : Dsq: Calculating The Perimeter Of A Quadrilateral

Consider rectangle .

I) Side  is three fourths of side .

II) Side  is  meters long.

What is the perimeter of ?

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.

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.

Either statement is sufficient to answer the question.

Correct answer:

Both statements are needed to answer the question.

Explanation:

To find perimeter, we need to find the length of all the sides. Recall that rectangles are made up of two pairs of equal sides.

I) Relates one side to another non-equivalent side.

II) Gives us side , which must be equivalent to .

Use II) and I) to find all the side lengths, then add them up. Both are needed.

Recap:

Consider rectangle CONT

I) Side CO is three fourths of side ON

II) Side NT is 15.7 meters long

What is the perimeter of CONT? 

Because we are dealing with a rectangle, we know the following:

              

Find perimeter with:

Use I) and II) to write the following equation:

So:

And finally:

Example Question #4 : Dsq: Calculating The Perimeter Of A Quadrilateral

Find the perimeter of the rectangle.

Statement 1:  The area of the rectangle is 24.

Statement 2:  The diagonal of the rectangle is 5.

Possible Answers:

Correct answer:

Explanation:

Statement 1): The area of the rectangle is 24.

Write the area for a rectangle and substitute the value of the area.

The length and width of the rectangle are unknown, and each set of dimensions will provide a different perimeter.  This statement is insufficient to find the perimeter of the rectangle.

Statement 2): The diagonal of the rectangle is 5.

Given the diagonal of the rectangle, the Pythagorean Theorem can be used to solve for the diagonal.  Express the equation in terms of length and width.

Similar to the case in Statement 1), both the length and width are unknown, and the equation by itself is insufficient to solve for the perimeter of the rectangle.

Attempting to use both equations:  and  to solve for length and width will yield complex numbers as part of the solution.

Therefore:

Example Question #6 : Other Quadrilaterals

Is parallelogram  a rectangle?

Statement 1: 

Statement 2: 

Possible Answers:

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 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:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Any two consecutive angles of a parallelogram are supplementary, so if one angle has measure , all angles can be proven to have measure . This is the definition of a rectangle. Statement 1 therefore proves the parallelogram to be a rectangle.

Also, a parallelogram is a rectangle if and only if its diagonals are congruent, which is what Statement 2 asserts. 

From either statement, it follows that parallelogram  is a rectangle.

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