ISEE Upper Level Quantitative Reasoning - How to find the volume of a sphere

is a positive number. Which is the greater quantity?

(A) The volume of a cube with edges of length

(B) The volume of a sphere with radius

(A) is greater

(B) is greater

(A) and (B) are equal

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

Explanation

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

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

$\frac{9}{2} \pi \textrm{ ft}^{3}$

$9 \pi \textrm{ ft}^{3}$

$18 \pi \textrm{ ft}^{3}$

$36 \pi \textrm{ ft}^{3}$

$3 \pi \textrm{ ft}^{3}$

Explanation

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

$V = \frac{4}{3} \pi r^{3}$

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

$V = \frac{4}{3}\cdot \frac{3}{2} \cdot \frac{3}{2} \cdot \frac{3}{2} \cdot \pi\left$

$V = \frac{1}{1}\cdot \frac{1}{1} \cdot \frac{3}{1} \cdot \frac{3}{2} \cdot \pi\left$

$V = \frac{9}{2} \pi$

Find the volume of a sphere with a diameter of 12in.

$288\pi \text{ in}^3$

$144\pi \text{ in}^3$

$256\pi \text{ in}^3$

$96\pi \text{ in}^3$

$200\pi \text{ in}^3$

Explanation

To find the volume of a sphere, we will use the following formula:

$V = \frac{4}{3} \cdot \pi \cdot r^3$

where r is the radius of the sphere.

Now, we know the diameter of the sphere is 12in. We also know the diameter is two times the radius. Therefore, the radius is 6in.

Knowing this, we can substitute into the formula. We get

$V = \frac{4}{3} \cdot \pi \cdot (6\text{in})^3$

$V = \frac{4}{3} \cdot \pi \cdot 6\text{in} \cdot 6\text{in} \cdot 6\text{in}$

Now, we can simplify before we multiply to make things easier. The 3 and a 6 can both be divided by 3. So, we get

$V = \frac{4}{1} \cdot \pi \cdot 2\text{in} \cdot 6\text{in} \cdot 6\text{in}$

$V = 4 \cdot \pi \cdot 72\text{in}^3$

$V = 288\pi \text{ in}^3$

Which is the greater quantity?

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

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

(a) is greater.

(b) is greater.

(a) and (b) are equal.

It is impossible to tell from the information given.

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.

You have a ball with a radius of 12 cm, what is its volume?

$2304 \pi cm^3$

$144 \pi cm^3$

$192 \pi cm^3$

$404 \pi cm^3$

Explanation

You have a ball with a radius of 12 cm, what is its volume?

The volume of a sphere can be found via the following formula:

$V_{sphere}=\frac{4}{3}\pi r^3$

We know our radius, so all we need to do is plug in and simplify:

$V_{sphere}=\frac{4}{3}\pi (12cm)^3=2304 \pi cm^3$

So we have our answer:

$2304 \pi cm^3$

Find the volume of a sphere with a diameter of 18in.

$972\text{in}^3$

$324\text{in}^3$

$108\text{in}^3$

$594\text{in}^3$

$288\text{in}^3$

Explanation

To find the volume of a sphere, we will use the following formula:

$V = \frac{4}{3} \cdot r^3$

where r is the radius of the sphere.

Now, we know the diameter of the sphere is 18in. We also know the diameter is two times the radius. Therefore, the radius is 9in.

Knowing this, we can substitute into the formula. We get

$V = \frac{4}{3} \cdot \pi \cdot (9\text{in})^3$

$V = \frac{4}{3} \cdot \pi \cdot 9\text{in} \cdot 9\text{in} \cdot 9\text{in}$

Now, we can simplify before we multiply to make things easier. The 3 and a 9 can both be divided by 3. So, we get

$V = \frac{4}{1} \cdot \pi \cdot 3\text{in} \cdot 9\text{in} \cdot 9\text{in}$

$V = 4 \cdot \pi \cdot 243\text{in}^3$

$V = 972\pi \text{ in}^3$

Which is the greater quantity?

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

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

(a) is greater.

(b) is greater.

(a) and (b) are equal.

It is impossible to tell from the information given.

Explanation

The radius of the sphere is one half of its diameter of one foot, which is six inches, so substitute :

$V = \frac{4}{3} \pi r ^{3}$

$V = \frac{4}{3} \pi \cdot 6 ^{3}$

$V = \frac{4}{3} \pi \cdot 216$

$V = 288 \pi \approx 288 \cdot 3.14 = 904.32$ cubic inches,

which is greater than $864 \textrm{ in}^{3}$ .

A spherical buoy has a radius of 5 meters. What is the volume of the buoy?

$166\frac{2}{3}\pi m^3$

$165 \pi m^3$

$166\frac{2}{3} m^3$

$16\frac{2}{3}\pi m^3$

Explanation

A spherical buoy has a radius of 5 meters. What is the volume of the buoy?

To find the volume of a sphere, use the following formula:

$V_{sphere}=\frac{4}{3}\pi r^3$

All we have to do is plug in 5 meters and simplify:

$V_{sphere}=\frac{4}{3}\pi (5m)^3=\frac{4}{3}\pi*125m^3=166\frac{2}{3}\pi m^3$

You have a wooden ball which you are going to paint. If the radius is 12 inches, what is the volume of the ball?

$2304\pi in^3$

$1728\pi in^3$

$576 \pi in^3$

Explanation

You have a wooden ball which you are going to paint. If the radius is 12 inches, what is the volume of the ball?

Alright, let's begin with the volume of a sphere formula:

$V_{sphere}=\frac{4}{3}\pi r^3$

Now, plug in 12 and simplify:

$V_{sphere}=\frac{4}{3}\pi(12in)^3=\frac{4}{3}\pi*1728in^3=2304\pi in^3$

Find the volume of a sphere with a diameter of 6cm.

$36\pi \text{ cm}^3$

$108\pi \text{ cm}^3$

$54\pi \text{ cm}^3$

$63\pi \text{ cm}^3$

$72\pi \text{ cm}^3$

Explanation

To find the volume of a sphere, we will use the following formula

$V = \frac{4}{3} \pi r^3$

where r is the radius of the sphere.

Now, we know the diameter of the sphere is 6cm. We also know the diameter is two times the radius. Therefore, the radius is 3cm.

So, we get

$V = \frac{4}{3} \cdot \pi \cdot (3\text{cm})^3$

$V = \frac{4}{3} \cdot \pi \cdot 27\text{cm}^3$

$V = \frac{4}{3} \cdot \frac{27\text{cm}^3}{1} \cdot \pi$

$V = \frac{4}{1} \cdot \frac{9\text{cm}^3}{1} \cdot \pi$

$V = \frac{4 \cdot 9\text{cm}^3}{1 \cdot 1} \cdot \pi$

$V = \frac{36\text{cm}^3}{1} \cdot \pi$

$V = 36\pi \text{ cm}^3$

How to find the volume of a sphere

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