ISEE Upper Level Quantitative : Plane Geometry

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

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Example Questions

Example Question #131 : Isee Upper Level (Grades 9 12) Quantitative Reasoning

In Pentagon ,

The other four angles are congruent to one another.

What is ?

Possible Answers:

It is impossible for this pentagon to exist.

Correct answer:

Explanation:

The degree measures of a pentagon, which has five angles, total .

.

Let . Then since the other three angles all have the same measure as 

Therefore, we can set up, and solve for  in, the equation

Example Question #132 : Isee Upper Level (Grades 9 12) Quantitative Reasoning

You are given pentagon 

Which is the greater quantity?

(A) 

(B) 

Possible Answers:

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

(A) is greater

(A) and (B) are equal

(B) is greater

Correct answer:

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

Explanation:

It is impossible to tell, as scenarios can be constructed that would allow  to be less than, equal to, or greater than 108, keeping in mind that the sum of the degree measures of a pentagon is .

Case 1: The pentagon is regular, so all five angles are of the same measure:

This fits the conditions of the problem and makes the two quantities equal.

Case 2: 

The sum of the angle measures is therefore 

This also fits the conditions of the problem, and makes (B) greater.

Example Question #131 : Geometry

Angles

Note: Figure NOT drawn to scale

In the above figure,  and  are adjacent sides of a regular pentagon;  and  are adjacent sides of a regular hexagon. Which of the following is the greater quantity?

(a) 

(b) 

Possible Answers:

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

(b) is the greater quantity

(a) and (b) are equal

(a) is the greater quantity

Correct answer:

(a) is the greater quantity

Explanation:

Extend  as seen below:

Angles

, as an interior angle of a regular pentagon (five-sided polygon), has measure

.

Its exterior angle  has measure .

 

, as an interior angle of a regular hexagon (six-sided polygon), has measure

.

Its exterior angle  has measure .

Add the measures of  and  to get that of :

.

.

Example Question #133 : Isee Upper Level (Grades 9 12) Quantitative Reasoning

The clock in the classroom reads 5:00pm. What is the angle that the hands are forming?

Possible Answers:

Correct answer:

Explanation:

Since the clock is a circle, you can determine that the total number of degrees inside the circle is 360. Since a clock has 12 numbers, we can divide 360 by 12 to see what the angle is between two numbers that are right next to each other. Thus, we can see that the angle between two numbers right next to each other is . However, the clock is reading 5:00, so there are five numbers we have to take in to account. Therefore, we multiply 30 by 5, which gives us as our answer.

Example Question #134 : Isee Upper Level (Grades 9 12) Quantitative Reasoning

The time on a clock reads 5:00. What is the measure of the central angle formed by the hands of the clock?

Possible Answers:

Correct answer:

Explanation:

First, remember that the number of degrees in a circle is 360. Then, figure out how many degrees are in between each number on the face of the clock. Since there are 12 numbers, there are between each number. Since the time reads 5:00, multiply , which yields .

Example Question #1 : Circles

Chords 1

Refer to the above figure. Which is the greater quantity?

(a) 

(b) 3 

Possible Answers:

(b) is the greater quantity

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

(a) and (b) are equal

(a) is the greater quantity

Correct answer:

(b) is the greater quantity

Explanation:

If two chords intersect inside a circle, both chords are cut in a way such that the products of the lengths of the two chords formed in each are the same - in other words, 

or

Therefore, .

Example Question #2 : How To Find The Length Of A Chord

Secant

Figure NOT drawn to scale

In the above figure,  is the center of the circle, and  is a tangent to the circle. Also, the circumference of the circle is .

Which is the greater quantity?

(a) 

(b) 25

Possible Answers:

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

(a) and (b) are equal

(b) is the greater quantity

(a) is the greater quantity

Correct answer:

(a) and (b) are equal

Explanation:

 is a radius of the circle from the center to the point of tangency of , so 

,

and  is a right triangle. The length of leg  is known to be 24. The other leg  is a radius radius; we can find its length by dividing the circumference by :

The length hypotenuse, , can be found by applying the Pythagorean Theorem:

.

Example Question #3 : How To Find The Length Of A Chord

Chords 1

Figure NOT drawn to scale.

Refer to the above figure. Which is the greater quantity?

(a) 

(b) 7

Possible Answers:

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

(a) and (b) are equal

(b) is the greater quantity

(a) is the greater quantity

Correct answer:

(b) is the greater quantity

Explanation:

If two chords intersect inside a circle, both chords are cut in a way such that the products of the lengths of the two chords formed in each are the same - in other words, 

Solving for :

Since , it follows that , or .

Example Question #4 : How To Find The Length Of A Chord

 

Secant

In the above figure,  is a tangent to the circle.

Which is the greater quantity?

(a) 

(b) 32

Possible Answers:

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

(b) is the greater quantity

(a) and (b) are equal

(a) is the greater quantity

Correct answer:

(b) is the greater quantity

Explanation:

If a secant segment and a tangent segment are constructed to a circle from a point outside it, the square of the distance to the circle along the tangent is equal to the product of the distances to the two points on the circle along the secant; in other words,

Simplifying, then solving for :

 

To compare  to 32, it suffices to compare their squares: 

, so, applying the Power of a Product Principle, then substituting,

, so

it follows that

.

Example Question #5 : How To Find The Length Of A Chord

Secant

Figure NOT drawn to scale

In the above figure,  is a tangent to the circle.

Which is the greater quantity?

(a) 

(b) 8

Possible Answers:

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

(b) is the greater quantity

(a) and (b) are equal

(a) is the greater quantity

Correct answer:

(a) and (b) are equal

Explanation:

If a secant segment and a tangent segment are constructed to a circle from a point outside it, the square of the distance to the circle along the tangent is equal to the product of the distances to the two points on the circle intersected by the secant; in other words,

Simplifying and solving for :

Factoring out :

Either  - which is impossible, since  must be positive, or

, in which case .

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