GRE Math : Quadrilaterals

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #161 : Geometry

A rectangle has a length that is twice that of its height. If the perimeter of that rectangle is , what is its area?

Possible Answers:

Correct answer:

Explanation:

Based on our first sentence, we know:

The second sentence means:

, which is the same as:

Now, we can replace  with  in the second equation:

Therefore, 

Now, this means that:

If these are our values, then the area of the rectangle is:

Example Question #42 : Quadrilaterals

A rectangle with an area of 64 square units is one-fourth as wide as it is long. What is the perimeter of the rectangle?

Possible Answers:

Correct answer:

Explanation:

Begin by setting up a ratio of width to length for the rectangle. We know that the width is one-fourth the length, therefore 

.

Now, we can substitute W in the rectangle area formula with our new variable to solve for the length.

Solve for length:

Using the length, solve for Width:

Now, plug the length and width into the formula for the perimeter of a rectangle to solve:

The perimeter of the rectangle is 40.

 

Example Question #1 : How To Find If Rectangles Are Similar

The perimeter of a rectangle is 14, and the diagonal connecting two vertices is 5. 

Quantity A: 13

Quantity B: The area of the rectangle

Possible Answers:

Quantity B is greater.

The relationship between A and B cannot be determined.

Quantity A is greater.

The two quantities are equal.

Correct answer:

Quantity A is greater.

Explanation:

One potentially helpful first step is to draw the rectangle described in the problem statement:

Gre rectangle

After that, it's a matter of using the other information given. The perimeter is given as 14, and can be written in terms of the length and width of the rectangle:

Furthermore, notice that the diagonal forms the hypotenuse of a right triangle. The Pythagorean Theorem may be applied:

This provides two equations and two unknowns. Redefining the first equation to isolate  gives:

Plugging this into the second equation in turn gives:

Which can be reduced to:

or

Note that there are two possibile values for ; 3 or 4. The one chosen is irrelevant. Choosing a value 3, it is possible to then find a value for :

This in turn allows for the definition of the rectangle's area:

So Quantity B is 12, which is less than Quantity A.

Example Question #163 : Geometry

One rectangle has sides of  and . Which of the following pairs could be the sides of a rectangle similar to this one?

Possible Answers:

 and 

 and 

 and 

 and 

Correct answer:

 and 

Explanation:

For this problem, you need to find the pair of sides that would reduce to the same ratio as the original set of sides. This is a little tricky at first, but consider the set:

 and 

For this, you have:

Now, if you factor out , you have:

Thus, the proportions are the same, meaning that the two rectangles would be similar.

Example Question #162 : Plane Geometry

One rectangle has a height of  and a width of . Which of the following is a possible perimeter of a similar rectangle, having one side that is ?

Possible Answers:

Correct answer:

Explanation:

Based on the information given, we know that  could be either the longer or the shorter side of the similar rectangle. Similar rectangles have proportional sides. We might need to test both, but let us begin with the easier proportion, namely:

 as 

For this proportion, you really do not even need fractions. You know that  must be .

This means that the figure would have a perimeter of 

Luckily, this is one of the answers!

Example Question #1361 : Gre Quantitative Reasoning

What is the perimeter of a square that has an area of 81?

Possible Answers:

18

36

9

40.5

Correct answer:

36

Explanation:

36

A square has four equal sides and its area = side2. Therefore, you can find the side length by taking the square root of the area √81 = 9. Then, find the perimeter by multiplying the side length by 4:

4 * 9 = 36 

Example Question #41 : Quadrilaterals

Geometry_2

The radius of the circle is 2 inches. What is the perimeter of the inscribed square? 

Possible Answers:

Correct answer:

Explanation:

The center of an inscribed square lies on the center of the circle. Thus, the line joining the center to a vertex of the square is also the radius. If we join the center with two adjacent vertices we can create a 45-45-90 right isosceles triangle, where the diagonal of the square is the hypotenuse. Since the radius is 2, the hypotenuse (a side of the square) must be  .

Finally, the perimeter of a square is

Example Question #1363 : Gre Quantitative Reasoning

Semicirclesquare

The diagram above represents a square ABCD with a semi-circle directly attached to its side.  If the area of the figure is 16 + 2π, what is its outer perimeter?

Possible Answers:

12 + 2π

16

None of the other answers

20π

16 + 2π

Correct answer:

12 + 2π

Explanation:

We know that our area can be represented by the following equation:

Instead of solving the algebra, you should immediately note several things.  16 = 42 and 4 = 22. If the side of the square is 4, then s = 4 would work out as:

 which is just what we need.

With s = 4, we know that 3 sides of our figure will have a perimeter of 12.  The remaining semicircle will be one half of the circumference of a circle with diameter of 4; therefore it will be 0.5 * 4 * π or 2π.

Therefore, the outer perimeter of our figure is 12 + 2π.

Example Question #1 : Squares

A square table has an area of  square centimeters and a perimeter of  centimeters.

If , what is the perimeter of the square?

Possible Answers:

Correct answer:

Explanation:

We start by writing the equations for the area and perimeter in terms of a side of length s.

Then, substitute both of these expressions into the given equation to solve for side length.

Finally, since four sides make up the perimeter, we substitue s back into our perimeter equation and solve for P.

Example Question #2 : How To Find The Perimeter Of A Square

The diagonal of square  is  feet. Approximately how long in inches is the perimeter of square ?

Possible Answers:

Correct answer:

Explanation:

First we must convert to inches.

The diagonal of a square divides the square into two isosceles-right triangles. Using the Pythagorean Theorem, we know that , where x is equal to the length of one side of the square.

This gives us .

Therefore, the perimeter of square  is equal to .

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