anonymous 5 years ago The celestial sphere shown at right has radius 9 inches. The planet in the sphere’s center has radius 3 inches. What is the ratio of the volume of the planet to the volume of the celestial sphere? What is the ratio of the surface area of the planet to the surface area of the celestial sphere?

1. anonymous

What is the formula for the volume of a sphere?

2. anonymous

4/3 pi3 right

3. anonymous

4/3 pi r^3

4. anonymous

well find the volume of each one first where the first volume has r=9 and the second has r=3 Why do we want the volume? Well we want to compare them right.

5. anonymous

i have for r=9 is 972pi3

6. anonymous

and r=3 is 36pi3

7. anonymous

Looks right but Im wondering where the 3 came from :P in pi3 I think you put it in by mistake.

8. anonymous

you know what ratio is right? basically a fraction and fractions is when you divide. You have to values so you divide one value with the other and you have the ratio

9. anonymous

so that mean 1:3 right?

10. anonymous

is $\frac{972\pi}{36\pi}$ 1:3?

11. anonymous

so i got 27

12. anonymous

if tha's what is then yes for the volume. Do the same for surface area. Find the formula for surface area and use r=9 and r=3

13. anonymous

324pi and 36pi