What is the index of refraction of this substance?

The speed of light in a certain substance is 79.0% of its value in water.
What is the index of refraction of this substance?

Here's what I've done so far:

(3.0*10^8 m/s)(0.79) because its 79%.
In water, the n=1.003.

I'm not sure where to go from there.
Any help would be greatly appreciated!

Redbelly98
Staff Emeritus
Homework Helper
The speed of light in a certain substance is 79.0% of its value in water.
What is the index of refraction of this substance?

Here's what I've done so far:

(3.0*10^8 m/s)(0.79) because its 79%.
In water, the n=1.003.
No, that's n for air.
n for water is ____?
The speed of light in water is ____?

correction:
n=1.33
and the speed of light in water (3x10^8)/(1.33)=2.25x10^8

Redbelly98
Staff Emeritus
Homework Helper
That's right. And:
The speed of light in a certain substance is 79.0% of its value in water.
Hope that's enough.

Since 79%, mulitplying (2.26x10^8)(0.79)= 1.78x10^8.
Correct?

Redbelly98
Staff Emeritus