GMAT Math : Calculating the area of a square

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #1 : Calculating The Area Of A Square

Write, in terms of \displaystyle N, the perimeter of a square whose area is \displaystyle N^{2 } - 6N + 9

Possible Answers:

\displaystyle 4N-36

\displaystyle N^{2}-9

\displaystyle 4N-24

\displaystyle 4N-12

\displaystyle N^{2}-12

Correct answer:

\displaystyle 4N-12

Explanation:

To find the perimeter of a square given its area, take the square root of the area to find its sidelength; then, multiply that sidelength by 4.

\displaystyle N^{2 } - 6N + 9 is a perfect square trinomial, since \displaystyle \left (\frac{-6}{2} \right )^{2} =(-3)^{2}= 9

so its square root is \displaystyle \sqrt{N^{2 } - 6N + 9} = N - 3, the sidelength.

Multiply this by 4 to get the perimeter: \displaystyle 4 \left (N - 3 \right ) = 4N - 12

Example Question #1 : Squares

If the diagonal of a square room is \displaystyle \frac{x}{2}. What is the area of the room?

Possible Answers:

\displaystyle \frac{x^2}{4}

\displaystyle \frac{x^2}{2}

\displaystyle x^2

\displaystyle \frac{x^2}{8}

Correct answer:

\displaystyle \frac{x^2}{8}

Explanation:

Cutting the triangle in half yields a right triangle with the diagonal becoming the hypotenuse and the other two legs being the sides of the square. Using the Pythagorean Theorem, we can solve for the other legs of the triangle.

\displaystyle a^2+b^2=c^2

Since both sides of the square are equal to eachother, \displaystyle a=b, therefore:

\displaystyle a^2+a^2=c^2

\displaystyle 2a^2=\left(\frac{x}{2}\right)^2

\displaystyle 2a^2= \frac{x^2}{4}

\displaystyle a^2=\frac{x^2}{8}

\displaystyle a= \frac{x}{\sqrt{8}}

To find the area of the square:

\displaystyle A=s^2 with leg \displaystyle a being one of the sides

\displaystyle A= \left(\frac{x}{\sqrt{8}}\right)^2

\displaystyle A=\frac{x^2}{8}

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 160,000\textup{ yd} ^{2}

\displaystyle 20,000 \textup{ yd} ^{2}

\displaystyle 100,000\textup{ yd} ^{2}

\displaystyle 90,000\textup{ yd} ^{2}

\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:

\displaystyle 352^{2} = 123,904 \textup{ ft} ^{2}

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:

\displaystyle 7,500 \textup{ cm}^{ 2}

\displaystyle 5,175 \textup{ cm}^{ 2}

\displaystyle 5,625 \textup{ cm}^{ 2}

\displaystyle 6,400 \textup{ cm}^{ 2}

\displaystyle 3,600 \textup{ cm}^{ 2}

Correct answer:

\displaystyle 5,625 \textup{ cm}^{ 2}

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 #2 : Calculating The Area Of A Square

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}.

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