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

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Example Question #11 : Squares

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

Possible Answers:

Correct answer:

Explanation:

A square being a rhombus, its area can be determined by taking half the product of the lengths of its (congruent) diagonals:

Example Question #21 : Squares

The lengths of the sides of ten squares form an arithmetic sequence. One side of the smallest square measures sixty centimeters; one side of the second-smallest square measures one meter. 

Give the area of the largest square, rounded to the nearest square meter.

Possible Answers:

24 square meters

20 square meters

22 square meters

18 square meters

16 square meters

Correct answer:

18 square meters

Explanation:

Let  be the lengths of the sides of the squares in meters.  and , so their common difference is

The arithmetic sequence formula is 

The length of a side of the largest square - square 10 - can be found by substituting :

 

The largest square has sides of length 4.2 meters, so its area is the square of this, or  square meters.

Of the choices, 18 square meters is closest.

Example Question #22 : Squares

The areas of six squares form an arithmetic sequence. The smallest square has perimeter 16; the second smallest square has perimeter 20. Give the area of the largest of the six squares.

Possible Answers:

Correct answer:

Explanation:

The two smallest squares have perimeters 16 and 20, so their sidelengths are one fourth of these, or, respectively, 4 and 5. Their areas are the squares of these, or, respectively, 16 and 25. Therefore, in the arithmetic sequence,

and the common difference is .

The area of the th smallest square is

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

Example Question #221 : Plane Geometry

Which is the greater quantity?

(a) The area of a square with sides of length  meters

(b) The area of a square with perimeter  centimeters

Possible Answers:

(a) and (b) are equal

(b) is the greater quantity

(a) is the greater quantity

It cannot be determined which of (a) and (b) is greater

Correct answer:

(a) is the greater quantity

Explanation:

A square with perimeter  centimeters has sides of length one-fourth of this, or  centimeters. Since one meter is equal to 100 centimeters, divide by 100 to get the equivalent in meters - this is 

meters.

The square in (b) has sidelength less than that of the square in (a), so its area is also less than that in (a).

Example Question #11 : How To Find The Area Of A Square

On the coordinate plane, Square A has as one side a segment with its endpoints at the origin and at the point with coordinates . Square B has as one side a segment with its endpoints at the origin and at the point with coordinates  and  are both positive numbers and . Which is the greater quantity?

(a) The area of Square A

(b) The area of Square B

Possible Answers:

(a) and (b) are equal

(b) is the greater quantity

(a) is the greater quantity

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

Correct answer:

(a) and (b) are equal

Explanation:

The length of a segment with endpoints  and  can be found using the distance formula with :

The length of a segment with endpoints  and  can be found using the distance formula with :

 

The sides are of equal length, so the squares have equal area. Note that the fact that  is irrelevant to the question.

Example Question #231 : Plane Geometry

On the coordinate plane, Square A has as one side a segment with its endpoints at the origin and at the point with coordinates . Square B has as one side a segment with its endpoints at the origin and at the point with coordinates  and  are both positive numbers and . Which is the greater quantity?

(a) The area of Square A

(b) The area of Square B

Possible Answers:

(a) is the greater quantity

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

(b) is the greater quantity

(a) and (b) are equal

Correct answer:

(b) is the greater quantity

Explanation:

The length of a segment with endpoints  and  can be found using the distance formula with :

This is the length of one side of Square A; the area of the square is the square of this, or .

 

By similar reasoning, the length of a segment with endpoints  and  is

and the area of Square B is 

.

 

Since , and both are positive, it follows that 

 

Square B has the greater area.

 

 

Example Question #21 : Squares

On the coordinate plane, Square A has as one side a segment with its endpoints at the origin and at the point with coordinates . Square B has as one side a segment with its endpoints at the origin and at the point with coordinates  and  are both positive numbers. Which is the greater quantity?

(a) The area of Square A

(b) The area of Square B

Possible Answers:

(a) is the greater quantity

(a) and (b) are equal

(b) is the greater quantity

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

Correct answer:

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

Explanation:

It can be proved that the given information is insufficient to answer the question by looking at two cases.

 

Case 1: 

Square A has as a side a segment with endpoints at  and , the length of which can be found using the distance formula with :

This is the length of one side of Square A; the area of the square is the square of this, or 52.

Square B has as a side a segment with endpoints at  and , the length of which can be found the same way:

This is the length of one side of Square B; the area of the square is the square of this, or 50. This makes Square A the greater in area.

 

Case 2: 

Square A has as a side a segment with endpoints at  and ; this was found earlier to be a square of area 50.

Square B has as a side a segment with endpoints at  and , the length of which can be found using the distance formula with :

This is the length of one side of Square B; the area of the square is the square of this, or 52. This makes Square B the greater in area.

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