GMAT Math : Quadrilaterals

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #2 : Calculating The Area Of A Square

A square plot of land has perimeter 1,200 feet. Give its area in square yards.

Possible Answers:

\displaystyle 10,000 \textrm{ yd} ^{2}

Correct answer:

\displaystyle 10,000 \textrm{ yd} ^{2}

Explanation:

The length of one side of the square is \displaystyle 1,200 \div 4 = 300 feet, or \displaystyle 300 \div 3 = 100 yards. Square this to get the area in square yards:

\displaystyle A =100^{2} =10,000 square yards.

Example Question #3 : Calculating The Area Of A Square

A square, a regular pentagon, and a regular hexagon have the same sidelength. The sum of their perimeters is one mile. What is the area of the square?

Possible Answers:

\displaystyle 193,600\textrm{ ft}^{2}

\displaystyle 278,784\textrm{ ft}^{2}

\displaystyle 123,904\textrm{ ft}^{2}

\displaystyle 69,696\textrm{ ft}^{2}

\displaystyle 108,900\textrm{ ft}^{2}

Correct answer:

\displaystyle 123,904\textrm{ ft}^{2}

Explanation:

The square, the pentagon, and the hexagon have a total of 15 sides, all of which are of equal length; the sum of the lengths is one mile, or 5,280 feet, so the length of one side of any of these polygons is 

\displaystyle 5,280 \div 15 = 352 feet.

The square has area equal to the square of this sidelength:

Example Question #1 : Calculating The Area Of A Square

A square and a regular pentagon have the same perimeter. The length of one side of the pentagon is 60 centimeters. What is the area of the square?

Possible Answers:

Correct answer:

Explanation:

The regular perimeter has sidelength 60 centimeters and therefore perimeter \displaystyle 5 \times 60 = 300 centimeters. The square has as its sidelength \displaystyle 300 \div 4 = 75 centimeters and area \displaystyle 75 ^{2} = 5,625 square centimeters.

Example Question #1 : Calculating The Area Of A Square

Six squares have sidelengths 8 inches, 1 foot, 15 inches, 20 inches, 2 feet, and 25 inches. What is the sum of their areas?

Possible Answers:

\displaystyle 2,034 \textrm{ in}^{2}

\displaystyle 416\textrm{ in}^{2}

\displaystyle 4,068\textrm{ in}^{2}

\displaystyle 10,816\textrm{ in}^{2}

\displaystyle 1,319\textrm{ in}^{2}

Correct answer:

\displaystyle 2,034 \textrm{ in}^{2}

Explanation:

The areas of the squares are the squares of the sidelengths, so add the squares of the sidelengths. Since 1 foot is equal to 12 inches and 2 feet are equal to 24 inches, the sum of the areas is:

\displaystyle 8^{2} + 12 ^{2} + 15 ^{2} + 20 ^{2} + 24^{2} + 25^{2}

\displaystyle = 64 + 144 + 225 + 400 + 576 + 625

\displaystyle =2,034 square inches

Example Question #161 : Geometry

What polynomial represents the area of Square \displaystyle ABCD if \displaystyle AC = 2t + 5 ?

Possible Answers:

\displaystyle 2t ^{2} +\frac{ 25 }{2}

\displaystyle 2t ^{2} +10t + 25

\displaystyle 4t ^{2} +20t +25

\displaystyle 2t ^{2} +10t +\frac{ 25 }{2}

\displaystyle 4t ^{2} +25

Correct answer:

\displaystyle 2t ^{2} +10t +\frac{ 25 }{2}

Explanation:

As a square, \displaystyle ABCD is also a rhombus. The area of a rhombus is half the product of the lengths of its diagonals, one of which is \displaystyle \overline{AC }. Since the diagonals are congruent, this is equal to half the square of \displaystyle AC :

\displaystyle \frac{1}{2} \left (AC \right) ^{2}

\displaystyle = \frac{1}{2} \left (2t + 5 \right) ^{2}

\displaystyle = \frac{1}{2}\left [ \left (2t \right) ^{2} + 2\left (2t \right) \cdot 5 + 5^{2} \right ]

\displaystyle = \frac{1}{2}\left ( 4t ^{2} +20t + 25 \right )

\displaystyle = 2t ^{2} +10t +\frac{ 25 }{2}

Example Question #1 : Calculating The Area Of A Square

Given square FGHI, answer the following

Square1

If square \displaystyle FGHI represents the surface of an ancient arena discovered by archaeologists, what is the area of the arena?

Possible Answers:

\displaystyle 225 \:m^2

\displaystyle 45 \:m^2

\displaystyle 120 \:m^2

\displaystyle 60 \:m^2

\displaystyle 30 \:m^2

Correct answer:

\displaystyle 225 \:m^2

Explanation:

This problem requires us to find the area of a square. Don't let the story behind it distract you, it is simply an area problem. Use the following equation to find our answer:

\displaystyle Area=s^2=(15\:m)^2=225\:m^2

\displaystyle s is the length of one side of the square; in this case we are told that it is \displaystyle 15\:m, so we can solve accordingly!

Example Question #51 : Quadrilaterals

Squares

Note: Figure NOT drawn to scale

Refer to the above figure, which shows Square \displaystyle ABCD and Square \displaystyle WXYZ\displaystyle BW = 1 and Square \displaystyle ABCD has area 49. Give the area of Square \displaystyle WXYZ.

Possible Answers:

\displaystyle 37

\displaystyle 49- \sqrt{6}

\displaystyle 49-2\sqrt{6}

\displaystyle 49-4\sqrt{6}

\displaystyle 43

Correct answer:

\displaystyle 37

Explanation:

Square \displaystyle ABCD has area 49, so each of its sides has as its length the square root of 49, or 7. Each side of Square \displaystyle WXYZ is therefore a hypotenuse of a right triangle with legs 1 and \displaystyle 7-1 = 6, so each sidelength, including \displaystyle WX, can be found using the Pythagorean Theorem:

\displaystyle WX = \sqrt{(WB)^{2}+(BX)^{2}}

\displaystyle WX = \sqrt{1^{2}+6^{2}} = \sqrt{1 +36} = \sqrt{37}

The square of this, which is 37, is the area of Square \displaystyle WXYZ.

Example Question #51 : Quadrilaterals

Squares

Note: Figure NOT drawn to scale

Refer to the above figure, which shows Square \displaystyle ABCD and Square \displaystyle WXYZ\displaystyle BW = 1 and Square \displaystyle WXYZ has area 25. Give the area of Square \displaystyle ABCD.

Possible Answers:

\displaystyle 25+4\sqrt{6}

\displaystyle 31

\displaystyle 25 + 8\sqrt{6}

\displaystyle 37

\displaystyle 25 + 2\sqrt{6}

Correct answer:

\displaystyle 25+4\sqrt{6}

Explanation:

Square \displaystyle WXYZ has area 25, so each side has length the square root of 25, or 5. 

Specifically, \displaystyle WX = 5, and, as given, \displaystyle BW = 1.

Since \displaystyle \bigtriangleup WBX is a right triangle with hypotenuse \displaystyle \overline{WX} and legs \displaystyle \overline{BW} and \displaystyle \overline{BX}\displaystyle BX can be found using the Pythagorean Theorem:

\displaystyle BX = \sqrt{(WX)^{2}-(BW)^{2}}

\displaystyle = \sqrt{5^{2}-1^{2}}

\displaystyle = \sqrt{25-1}

\displaystyle = \sqrt{24}

\displaystyle =\sqrt{4} \cdot \sqrt{6}

\displaystyle = 2\sqrt{6}

 

The area of \displaystyle \bigtriangleup WBX is 

\displaystyle \frac{1}{2} \cdot BW \cdot BX = \frac{1}{2} \cdot 1 \cdot 2 \sqrt{6} = \sqrt{6}

 

Since all four triangles, by symmetry, are congruent, all have this area. the area of Square \displaystyle ABCD is the area of Square \displaystyle WXYZ plus the areas of the four triangles, or \displaystyle 25 + 4\sqrt{6}.

Example Question #161 : Geometry

Squares

Note: Figure NOT drawn to scale

Refer to the above figure, which shows Square \displaystyle ABCD and Square \displaystyle WXYZ. The ratio of \displaystyle BX to \displaystyle XC is 13 to 2. What is the ratio of the area of Square \displaystyle ABCD to that of Square \displaystyle WXYZ?

Possible Answers:

\displaystyle 225:173

\displaystyle 17:15

\displaystyle 15:13

\displaystyle 225:221

\displaystyle 225:169

Correct answer:

\displaystyle 225:173

Explanation:

To make this easier, assume that \displaystyle BX = 13 and \displaystyle BW=CX = 2 - the reasoning generalizes. Then Square \displaystyle ABCD has sidelength 15 and area \displaystyle 15^{2}= 225. The sidelength of Square \displaystyle WXYZ, each side being a hypotenuse of a right triangle with legs 2 and 13, is 

\displaystyle \sqrt{2^{2}+13^{2}}= \sqrt{4+169} = \sqrt{173}.

The square of this, 173, is the area of Square \displaystyle WXYZ.

The ratio is \displaystyle 225:173.

Example Question #171 : Geometry

Squares

Note: Figure NOT drawn to scale

Refer to the above figure, which shows Square \displaystyle ABCD and Square \displaystyle WXYZ.  The ratio of \displaystyle BX to \displaystyle XC is 7 to 1.

Which of these responses comes closest to what percent the area of Square \displaystyle WXYZ is of that of Square \displaystyle ABCD?

 

Possible Answers:

\displaystyle 75 \%

\displaystyle 90 \%

\displaystyle 85 \%

\displaystyle 70 \%

\displaystyle 80 \%

Correct answer:

\displaystyle 80 \%

Explanation:

To make this easier, assume that \displaystyle BX = 7 and \displaystyle BW = XC = 1; the results generalize. 

Each side of Square \displaystyle ABCD has length 8, so the area of Square \displaystyle ABCD is 64. 

Each of the four right triangles has legs 7 and 1, so each has area \displaystyle \frac{1}{2} \cdot 1 \cdot 7 = 3\frac{1}{2}; Square \displaystyle WXYZ has area four times this subtracted from the area of Square \displaystyle ABCD, or

\displaystyle 64 - 4 \cdot 3 \frac{1}{2} = 50.

The area of Square \displaystyle WXYZ is

\displaystyle \frac{50}{64} \times 100 \% = 78 \frac{1}{8} \%

of that of Square \displaystyle ABCD.

Of the five choices, 80% comes closest.

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