The radius of the large sphere is three times longer than the radius of the small sphere. How many times the volume of the large sphere is the volume of the small sphere?

A. [tex]$\frac{1}{27}$[/tex]
B. [tex]$\frac{1}{18}$[/tex]
C. [tex]$\frac{1}{9}$[/tex]
D. [tex]$\frac{1}{3}$[/tex]



Answer :

To solve this problem, let's first recall the formula for the volume of a sphere:

[tex]\[ V = \frac{4}{3} \pi r^3 \][/tex]

where [tex]\( V \)[/tex] is the volume and [tex]\( r \)[/tex] is the radius of the sphere.

### Step-by-Step Solution:

1. Define the Radii:
- Let the radius of the small sphere be [tex]\( r \)[/tex].
- Since the radius of the large sphere is three times that of the small sphere, the radius of the large sphere will be [tex]\( 3r \)[/tex].

2. Calculate the Volume of the Small Sphere:
- Using the formula for the volume of a sphere:
[tex]\[ V_{\text{small}} = \frac{4}{3} \pi r^3 \][/tex]

3. Calculate the Volume of the Large Sphere:
- Similarly, for the large sphere with radius [tex]\( 3r \)[/tex]:
[tex]\[ V_{\text{large}} = \frac{4}{3} \pi (3r)^3 \][/tex]
- Simplify the expression:
[tex]\[ V_{\text{large}} = \frac{4}{3} \pi (27r^3) \][/tex]
[tex]\[ V_{\text{large}} = 27 \cdot \frac{4}{3} \pi r^3 \][/tex]
[tex]\[ V_{\text{large}} = 27 \cdot V_{\text{small}} \][/tex]

Hence, the volume of the large sphere is 27 times the volume of the small sphere.

4. Determine the Ratio of the Volumes:
- The question asks for the ratio of the volume of the large sphere to the volume of the small sphere.
- As derived:
[tex]\[ \text{Volume ratio} = \frac{V_{\text{large}}}{V_{\text{small}}} = 27 \][/tex]

Therefore, the volume of the large sphere is 27 times the volume of the small sphere.

Given the multiple-choice options are fractions, this affirmation suggests we need the inverse of the ratio to see if the answer fits one of the provided choices. The reciprocal of 27 is [tex]\(\frac{1}{27}\)[/tex].

So, the correct choice is:

[tex]\(\frac{1}{27}\)[/tex]

This means:
[tex]\[\text{The correct answer is} \ \boxed{\frac{1}{27}}.\][/tex]