ISEE Upper Level Quantitative : ISEE Upper Level (grades 9-12) Quantitative Reasoning

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

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Example Questions

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

Which is the greater quantity?

(a) The surface area of a regular tetrahedron with edges of length 1

(b) 2

Possible Answers:

(b) is greater.

(a) and (b) are equal.

(a) is greater.

It is impossible to tell from the information given.

Correct answer:

(b) is greater.

Explanation:

A regular tetrahedron has four faces, each of which is an equilateral triangle. Therefore, its surface area, given sidelength \(\displaystyle s\), is 

\(\displaystyle A = 4 \cdot \frac{s^{2} \sqrt{3}}{4} = s^{2} \sqrt{3}\).

Substitute \(\displaystyle s = 1\) :

\(\displaystyle A = s^{2} \sqrt{3} =1^{2} \cdot \sqrt{3} = \sqrt{3}\)

\(\displaystyle \sqrt{3} \approx 1.7 < 2\), so (b) is greater.

Example Question #1 : How To Find The Radius Of A Sphere

The volume of a sphere is one cubic yard. Give its radius in inches.

Possible Answers:

\(\displaystyle \frac{ \sqrt{3 \pi } } {2 \pi} \textrm{ in}\)

\(\displaystyle \frac{ 18\sqrt[3]{6 \pi^{2}} } {\pi} \textrm{ in}\)

\(\displaystyle \frac{ 6\sqrt[3]{6 \pi^{2}} } {\pi} \textrm{ in}\)

\(\displaystyle \frac{ 18\sqrt{3 \pi } } {\pi} \textrm{ in}\)

\(\displaystyle \frac{ \sqrt[3]{6 \pi^{2}} } {2\pi}\textrm{ in}\)

Correct answer:

\(\displaystyle \frac{ 18\sqrt[3]{6 \pi^{2}} } {\pi} \textrm{ in}\)

Explanation:

The volume \(\displaystyle V\) of a sphere with radius \(\displaystyle r\) is 

\(\displaystyle V = \frac{4}{3} \pi r^{3}\) .

To find the radius in yards, we set \(\displaystyle V = 1\) and solve for \(\displaystyle r\).

\(\displaystyle 1 = \frac{4}{3} \pi r^{3}\)

\(\displaystyle \frac{3}{4} \cdot 1 =\frac{3}{4} \cdot \frac{4}{3} \pi r^{3}\)

\(\displaystyle \frac{3}{4} = \pi r^{3}\)

\(\displaystyle \frac{1}{\pi} \cdot \frac{3}{4} =\frac{1}{\pi} \cdot \pi r^{3}\)

\(\displaystyle \frac{3}{4\pi} = r^{3}\)

\(\displaystyle r = \sqrt[3]{ \frac{3}{4\pi} } = \sqrt[3]{ \frac{3\cdot 2 \pi^{2}}{4\pi \cdot 2 \pi^{2}} }= \sqrt[3]{ \frac{6 \pi^{2}}{8 \pi^{3}} } = \frac{ \sqrt[3]{6 \pi^{2}} } {2\pi}\) yards. 

 

Since the problem requests the radius in inches, multiply by 36:

\(\displaystyle 36 \times \frac{ \sqrt[3]{6 \pi^{2}} } {2\pi} = \frac{ 18\sqrt[3]{6 \pi^{2}} } {\pi}\)

 

Example Question #32 : Solid Geometry

In terms of \(\displaystyle \pi\), give the volume, in cubic feet, of a spherical tank with diameter 36 inches.

Possible Answers:

\(\displaystyle 3 \pi \textrm{ ft}^{3}\)

\(\displaystyle 9 \pi \textrm{ ft}^{3}\)

\(\displaystyle 36 \pi \textrm{ ft}^{3}\)

\(\displaystyle 18 \pi \textrm{ ft}^{3}\)

\(\displaystyle \frac{9}{2} \pi \textrm{ ft}^{3}\)

Correct answer:

\(\displaystyle \frac{9}{2} \pi \textrm{ ft}^{3}\)

Explanation:

36 inches = \(\displaystyle 36 \div 12 = 3\) feet, the diameter of the tank. Half of this, or \(\displaystyle \frac{3}{2}\) feet, is the radius. Set \(\displaystyle r = \frac{3}{2}\), substitute in the volume formula, and solve for \(\displaystyle V\):

\(\displaystyle V = \frac{4}{3} \pi r^{3}\)

\(\displaystyle V = \frac{4}{3} \pi\left \cdot \left( \frac{3}{2} \right ) ^{3}\)

\(\displaystyle V = \frac{4}{3}\cdot \frac{3}{2} \cdot \frac{3}{2} \cdot \frac{3}{2} \cdot \pi\left\)

\(\displaystyle V = \frac{1}{1}\cdot \frac{1}{1} \cdot \frac{3}{1} \cdot \frac{3}{2} \cdot \pi\left\)

\(\displaystyle V = \frac{9}{2} \pi\)

Example Question #1 : How To Find The Volume Of A Sphere

Which is the greater quantity?

(a) The volume of a sphere with radius \(\displaystyle t\)

(b) The volume of a cube with sidelength \(\displaystyle 2t\)

Possible Answers:

It is impossible to tell from the information given

(a) is greater

(b) is greater

(a) and (b) are equal

Correct answer:

(b) is greater

Explanation:

A sphere with radius \(\displaystyle t\) has diameter \(\displaystyle 2t\) and can be inscribed inside a cube of sidelength \(\displaystyle 2t\). Therefore, the cube in (b) has the greater volume.

Example Question #2 : How To Find The Volume Of A Sphere

Which is the greater quantity?

(a) The volume of a cube with sidelength  inches.

(b) The volume of a sphere with radius  inches.

Possible Answers:

(b) is greater.

It is impossible to tell from the information given.

(a) and (b) are equal.

(a) is greater.

Correct answer:

(a) is greater.

Explanation:

You do not need to calculate the volumes of the figures. All you need to do is observe that a sphere with radius  inches has diameter  inches, and can therefore be inscribed inside the cube with sidelength  inches. This give the cube larger volume, making (a) the greater quantity.

Example Question #3 : How To Find The Volume Of A Sphere

Which is the greater quantity? 

(a) The volume of a sphere with diameter one foot

(b) \(\displaystyle 864 \textrm{ in}^{3}\)

Possible Answers:

(a) is greater.

(b) is greater.

(a) and (b) are equal.

It is impossible to tell from the information given.

Correct answer:

(a) is greater.

Explanation:

The radius of the sphere is one half of its diameter of one foot, which is six inches, so substitute \(\displaystyle r = 6\):

\(\displaystyle V = \frac{4}{3} \pi r ^{3}\)

\(\displaystyle V = \frac{4}{3} \pi \cdot 6 ^{3}\)

\(\displaystyle V = \frac{4}{3} \pi \cdot 216\)

\(\displaystyle V = 288 \pi \approx 288 \cdot 3.14 = 904.32\) cubic inches,

which is greater than \(\displaystyle 864 \textrm{ in}^{3}\).

Example Question #4 : How To Find The Volume Of A Sphere

\(\displaystyle t\) is a positive number. Which is the greater quantity?

(A) The volume of a cube with edges of length \(\displaystyle 2t\)

(B) The volume of a sphere with radius \(\displaystyle t\)

Possible Answers:

(B) is greater

(A) and (B) are equal 

(A) is greater

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

Correct answer:

(A) is greater

Explanation:

No calculation is really needed here, as a sphere with radius \(\displaystyle t\) - and, subsequently, diameter \(\displaystyle 2t\) - can be inscribed inside a cube of sidelength \(\displaystyle 2t\). This makes (A), the volume of the cube, the greater.

Example Question #6 : Spheres

Which is the greater quantity?

(a) The radius of a sphere with surface area \(\displaystyle 36 \pi\)

(b) The radius of a sphere with volume \(\displaystyle 36 \pi\)

Possible Answers:

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

(a) is the greater quantity

(a) and (b) are equal

(b) is the greater quantity

Correct answer:

(a) and (b) are equal

Explanation:

The formula for the surface area of a sphere, given its radius \(\displaystyle r\), is 

\(\displaystyle A = 4 \pi r^{2}\)

The sphere in (a) has surface area \(\displaystyle 36 \pi\), so 

\(\displaystyle 36 \pi = 4 \pi r^{2}\)

\(\displaystyle 36 \pi\div 4 \pi = 4 \pi r^{2} \div 4 \pi\)

\(\displaystyle 9 = r^{2}\)

\(\displaystyle r = \sqrt{9} = 3\)

 

 

The formula for the volume of a sphere, given its radius \(\displaystyle r\), is

\(\displaystyle V = \frac{4}{3} \pi r^{3}\)

The sphere in (b) has volume \(\displaystyle 36 \pi\), so 

\(\displaystyle 36 \pi = \frac{4}{3} \pi r^{3}\)

\(\displaystyle \frac{3} {4} \cdot 36 \pi = \frac{3} {4} \cdot \frac{4}{3} \pi r^{3}\)

\(\displaystyle 27 \pi = \pi r^{3}\)

\(\displaystyle 27 \pi\div \pi = \pi r^{3} \div \pi\)

\(\displaystyle 27 = r^{3}\)

\(\displaystyle r = \sqrt[3]{27} = 3\)

 

The radius of both spheres is 3.

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

In terms of \(\displaystyle \pi\), give the surface area, in square inches, of a spherical water tank with a diameter of 20 feet.

Possible Answers:

\(\displaystyle 18,432,000\pi\textrm{ in}^{2}\)

\(\displaystyle 307,200\pi\textrm{ in}^{2}\)

\(\displaystyle 230,400 \pi\textrm{ in}^{2}\)

\(\displaystyle 2,304,000 \pi \textrm{ in}^{2}\)

\(\displaystyle 57,600 \pi\textrm{ in}^{2}\)

Correct answer:

\(\displaystyle 57,600 \pi\textrm{ in}^{2}\)

Explanation:

\(\displaystyle 20\) feet = \(\displaystyle 20 \times 12 = 240\) inches, the diameter of the tank; half of this, or 120 inches, is the radius. Set \(\displaystyle r = 120\), substitute in the surface area formula, and solve for \(\displaystyle A\):

\(\displaystyle A =4\pi r^{2}\)

\(\displaystyle A =4\pi \cdot 120^{2}\)

\(\displaystyle A =4\pi \cdot 14,400\)

\(\displaystyle A = 57,600 \pi\)

Example Question #331 : Isee Upper Level (Grades 9 12) Quantitative Reasoning

Which is the greater quantity?

(a) The surface area of a sphere with radius 1

(b) 12

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) is greater.

Explanation:

The surface area of a sphere can be found using the formula

\(\displaystyle A = 4\pi r^{2}\).

The surface area of the given sphere can be found by substituting \(\displaystyle r = 1\):

\(\displaystyle A = 4\pi \cdot 1^{2} = 4\pi\)

\(\displaystyle \pi > 3\) so \(\displaystyle 4 \times \pi >4 \times 3\), or \(\displaystyle 4\pi > 12\)

This makes (a) greater.

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