I am having a little bit of trouble finding the speed of light in a given medium when you are only supplied with the index of refraction. For example, I was given that n=1.36 in ethanol, and I had to find the speed of sound in ethanol. I know the equation for the index of refraction is n=c/v, but I am having problems with actually using it. For example, when only given that the index in a vacuum is 1.0, how do you know the speed, or do you use 300,000 km/s? Just a little bit confused here.