ISEE Upper Level Quantitative : Plane Geometry

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

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Example Questions

Example Question #1 : Quadrilaterals

The area of a square is .

Give the perimeter of the square.

Possible Answers:

Correct answer:

Explanation:

The length of one side of a square is the square root of its area. The polynomial representing the area of the square can be recognized as a perfect square trinomial:

Therefore, the square root of the area is

,

which is the length of one side.

The perimeter of the square is four times this length, or

.

Example Question #1 : Squares

The perimeters of six squares form an arithmetic sequence. The second-smallest square has sides that are two inches longer than those of the smallest square.

Which, if either, is the greater quantity?

(a) The perimeter of the third-smallest square

(b) The length of one side of the largest square

Possible Answers:

(a) and (b) are equal

(a) is greater

(b) is greater

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

Correct answer:

(a) is greater

Explanation:

Let the length of one side of the first square be . Then the length of one side of the second-smallest square is , and the perimeters of the squares are

and 

This makes the common difference of the perimeters 8 units.

The perimeters of the squares being in arithmetic progression, the perimeter of the th-smallest square is

Since , this becomes 

The perimeter of the third-smallest square is 

The perimeter of the largest, or sixth-smallest, square is

The length of one side of this square is one fourth of this, or

Therefore, we are comparing  and .

Since a perimeter must be positive,

;

also, .

Therefore, regardless of the value of ,

,

and 

,

making (a) the greater quantity.

Example Question #2 : Squares

The sidelength of a square is . Give its perimeter in terms of .

Possible Answers:

Correct answer:

Explanation:

The perimeter of a square is four times the length of a side, which here is :

Example Question #2 : Squares

A diagonal of a square has length . Give its perimeter. 

Possible Answers:

Correct answer:

Explanation:

The length of a side of a square can be determined by dividing the length of a diagonal by  - that is, . A diagonal has length , so the sidelength is

Multiply this by four to get the perimeter:

Example Question #1 : Squares

The perimeters of six squares form an arithmetic sequence. The smallest square has area 9; the second smallest square has area 25. Give the perimeter of the largest of the six squares.

Possible Answers:

None of the other responses gives the correct answer.

Correct answer:

Explanation:

The two smallest squares have areas 9 and 25, so their sidelengths are the square roots of these, or, respectively, 3 and 5. Their perimeters are the sidelengths multiplied by four, or, respectively, 12 and 20. Therefore, in the arithmetic sequence,

and the common difference is .

The perimeter of the th smallest square is

Setting , the perimeter of the largest (or sixth-smallest) square is

.

Example Question #4 : Squares

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

(a) The area of the square

(b)  square foot

Possible Answers:

(a) and (b) are equal.

(a) is greater.

(b) is greater.

It is impossible to tell form the information given.

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  feet. The area of the square is  square feet. , making (a) greater.

Example Question #211 : Plane Geometry

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:

(b) is greater.

(a) is greater.

It is impossible to tell from the information given.

(a) and (b) are equal.

Correct answer:

(a) and (b) are equal.

Explanation:

Let  be the sidelength of Square 1. Then the length of a diagonal of this square - which is  times this sidelength, or , by the  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 , and Square 2 has area , twice that of Square 1.

 

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

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

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

(A) is greater

Correct answer:

(A) is greater

Explanation:

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

 square inches.

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

 square inches.

The square has the greater area.

Example Question #3 : How To Find The Area Of A Square

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

Possible Answers:

Correct answer:

Explanation:

20 yards converts to  feet. The area of a square is the square of its sidelength, so the area in square feet is  square feet.

Example Question #1 : 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:

Correct answer:

Explanation:

The perimeter of a rectangle can be given by the formula

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

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

 square centimeters.

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

 centimeters; its area is therefore 

 square centimeters.

The area of Rectangle A is therefore 

that of Square B.

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