The index of refraction of a medium is defined as
[tex]n= \frac{c}{v} [/tex]
where
c is the speed of light in vacuum
v is the speed of light in the medium
For the medium in our problem, [tex]v=1.7 \cdot 10^8 m/s[/tex], so if we apply the previous formula we find the index of refraction of the medium:
[tex]n= \frac{c}{v}= \frac{3 \cdot 10^8 m/s}{1.7 \cdot 10^8 m/s} =1.76[/tex]
