ISEE Upper Level Quantitative : How to find the area of a square

Study concepts, example questions & explanations for ISEE Upper Level Quantitative

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Example Questions

Example Question #1 : How To Find The Area Of A Square

The perimeter of a square is one yard. Which is the greater quantity?

(a) The area of the square

(b) \(\displaystyle \frac{1}{2}\) square foot

Possible Answers:

(b) is greater.

It is impossible to tell form the information given.

(a) and (b) are equal.

(a) is greater.

Correct answer:

(a) is greater.

Explanation:

One yard is equal to three feet, so the length of one side of a square with this perimeter is \(\displaystyle \frac{3}{4}\) feet. The area of the square is \(\displaystyle \frac{3}{4}\times \frac{3}{4} = \frac{9}{16}\) square feet. \(\displaystyle \frac{9}{16} > \frac{1}{2}\), making (a) greater.

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

Square 1 is inscribed inside a circle. The circle is inscribed inside Square 2.

Which is the greater quantity?

(a) Twice the area of Square 1

(b) The area of Square 2

Possible Answers:

(a) is greater.

(a) and (b) are equal.

It is impossible to tell from the information given.

(b) is greater.

Correct answer:

(a) and (b) are equal.

Explanation:

Let \(\displaystyle s\) be the sidelength of Square 1. Then the length of a diagonal of this square - which is \(\displaystyle \sqrt{2}\) times this sidelength, or \(\displaystyle s \sqrt{2}\), by the \(\displaystyle 45^{\circ }-45^{\circ }-90^{\circ }\) Theorem - is the same as the diameter of this circle, which, in turn, is equal to the sidelength of Square 2. 

Therefore, Square 1 has area \(\displaystyle A = s^{2}\), and Square 2 has area \(\displaystyle A = \left ( s \sqrt{2 } \right )^{2} = 2s^{2}\), twice that of Square 1.

 

Example Question #211 : Plane Geometry

Which is the greater quantity?

(A) The area of a square with sidelength one foot

(B) The area of a rectangle with length nine inches and height fourteen inches

Possible Answers:

(A) and (B) are equal

(B) is greater

(A) is greater

It is impossible to determine which is greater from the information given

Correct answer:

(A) is greater

Explanation:

The area of a square is the square of its sidelength, which here is 12 inches:

\(\displaystyle A = 12^{2} = 144\) square inches.

The area of a rectangle is its length multiplied by its height, which, respectively, are 9 inches and 14 inches:

\(\displaystyle A = 9 \cdot 14 = 126\) square inches.

The square has the greater area.

Example Question #1 : How To Find The Area Of A Square

A square lawn has sidelength twenty yards. Give its area in square feet.

Possible Answers:

\(\displaystyle 2,800\textrm{ ft}^{2}\)

\(\displaystyle 4,200\textrm{ ft}^{2}\)

\(\displaystyle 3,600\textrm{ ft}^{2}\)

\(\displaystyle 3,200\textrm{ ft}^{2}\)

\(\displaystyle 4,000\textrm{ ft}^{2}\)

Correct answer:

\(\displaystyle 3,600\textrm{ ft}^{2}\)

Explanation:

20 yards converts to \(\displaystyle 20 \times3 = 60\) feet. The area of a square is the square of its sidelength, so the area in square feet is \(\displaystyle 60^{2} = 60 \times 60 = 3,600\) square feet.

Example Question #4 : How To Find The Area Of A Square

Rectangle A and Square B both have perimeter 2 meters. Rectangle A has width 25 centimeters. The area of Rectangle A is what percent of the area of Square B? 

Possible Answers:

\(\displaystyle 66 \frac{2}{3} \%\)

\(\displaystyle 80 \%\)

\(\displaystyle 83 \frac{1}{3} \%\)

\(\displaystyle 87 \frac{1}{2} \%\)

\(\displaystyle 75 \%\)

Correct answer:

\(\displaystyle 75 \%\)

Explanation:

The perimeter of a rectangle can be given by the formula

\(\displaystyle P = 2(L+W)\)

Rectangle A has perimeter 2 meters, which is equal to 200 centimeters, and width 25 centimeters, so the length is:

\(\displaystyle 2(L+W) = P\)

\(\displaystyle 2(L+25) = 200\)

\(\displaystyle 2L + 50= 200\)

\(\displaystyle 2L = 150\)

\(\displaystyle L = 75\)

The dimensions of Rectangle A are 75 centimeters and 25 centimeters, so its area is 

\(\displaystyle 75 \times 25 = 1,875\) square centimeters.

The sidelength of a square is one-fourth its perimeter, which here is 

\(\displaystyle \frac{200}{4} = 50\) centimeters; its area is therefore 

\(\displaystyle 50 ^{2} = 2,500\) square centimeters.

The area of Rectangle A is therefore 

\(\displaystyle \frac{1,875}{2,500} \times 100 = 75 \%\)

that of Square B.

Example Question #5 : How To Find The Area Of A Square

The sidelength of Square A is three-sevenths that of Square B. What is the ratio of the area of Square B to that of Square A?

Possible Answers:

\(\displaystyle 49 \textrm{ to } 9\)

\(\displaystyle 14\textrm{ to }3\)

None of the other answers give the correct ratio.

\(\displaystyle 9\textrm{ to }7\)

\(\displaystyle 7\textrm{ to }3\)

Correct answer:

\(\displaystyle 49 \textrm{ to } 9\)

Explanation:

Since the ratio is the same regardless of the sidelengths, then for simplicity's sake, assume the sidelength of Square B is 7. The area of Square B is therefore the square of this, or 49.

Then the sidelength of Square A is three-sevenths of 7, or 3. Its area is the square of 3, or 9. 

The ratio of the area of Square B to that of Square A is therefore 49 to 9.

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

Five squares have sidelengths one foot, two feet, three feet, four feet, and five feet.

Which is the greater quantity?

(A) The mean of their areas

(B) The median of their areas

Possible Answers:

(A) and (B) are equal

(B) is greater

It is impossible to tell which is greater from the information given

(A) is greater

Correct answer:

(A) is greater

Explanation:

The areas of the squares are:

\(\displaystyle 1^{2} = 1\) square foot

\(\displaystyle 2^{2} = 4\) square feet

\(\displaystyle 3^{2} = 9\) square feet

\(\displaystyle 4^{2}= 16\) square feet

\(\displaystyle 5^{2}= 25\) square feet

Therefore, we are comparing the mean and the median of the set \(\displaystyle \left \{ 1, 4, 9, 16, 25\right \}\).

The mean of this set is the sum divided by 5:

 \(\displaystyle (1 + 4 + 9 + 16 + 25) \div 5 = 55 \div 5 = 11\) 

The median is the middle element after arrangement in ascending order, which is 9.

This makes (A), the mean, greater.

Example Question #21 : Quadrilaterals

Four squares have sidelengths one meter, 120 centimeters, 140 centimeters, and 140 centimeters. Which is the greater quantity?

(A) The mean of their areas

(B) The median of their areas

Possible Answers:

It is impossible to tell which is greater from the information given

(B) is greater

(A) is greater

(A) and (B) are equal

Correct answer:

(B) is greater

Explanation:

The areas of the squares are:

\(\displaystyle 100 \cdot 100 = 10,000\) square centimeters (one meter being 100 centimeters)

\(\displaystyle 120 \cdot 120 = 14,400\) square centimeters

\(\displaystyle 140 \cdot 140 = 19,600\) square centimeters

\(\displaystyle 140 \cdot 140 = 19,600\) square centimeters

The mean of these four areas is their sum divided by four:

\(\displaystyle (10,000+14,400+19,600+19,600) \div 4\)

\(\displaystyle = 63,600 \div 4 =15,900\) square centimeters.

The median is the mean of the two middle values, or

\(\displaystyle ( 14,400+19,600 ) \div 2 = 34,000 \div 2 = 17,000\) square centimeters.

The median, (B), is greater.

Example Question #22 : Quadrilaterals

The perimeter of a square is \(\displaystyle 12x+16\). Give the area of the square in terms of \(\displaystyle x\).

Possible Answers:

\(\displaystyle 9x^{2}+24x + 16\)

\(\displaystyle 144x^{2} +384x+ 256\)

\(\displaystyle 144x^{2} + 256\)

\(\displaystyle 9x^{2} + 16\)

None of the other responses gives a correct answer.

Correct answer:

\(\displaystyle 9x^{2}+24x + 16\)

Explanation:

The length of one side of a square is one fourth its perimeter. Since the perimeter of the square is \(\displaystyle 12x+16\), the length of one side is

\(\displaystyle (12x+16) \div 4 = 3x+ 4\)

The area of the square is the square of this sidelength, or

\(\displaystyle ( 3x+ 4)^{2}= (3x)^{2}+ 2 \cdot 3x \cdot 4 + 4 ^{2} = 9x^{2}+24x + 16\)

Example Question #23 : Quadrilaterals

The sidelength of a square is \(\displaystyle 2^{x}\). Give its area in terms of \(\displaystyle x\).

Possible Answers:

\(\displaystyle 2 ^{x+1}\)

\(\displaystyle 2 ^{4 x}\)

\(\displaystyle 2 ^{x+4}\)

\(\displaystyle 2 ^{2 x}\)

\(\displaystyle 2 ^{x+2}\)

Correct answer:

\(\displaystyle 2 ^{2 x}\)

Explanation:

The area of a square is the square of its sidelength. Therefore, square \(\displaystyle 2^{x}\):

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

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