Blue light with a wavelength of 430 nm from a vacuum into a glass lens; and the index of refraction is found to be 1.65. The glass lens is replaced with a plastic lens. The index of refraction for the plastic lens is 1.54. In which one of the two lenses does the light have the greatest speed and what is that speed?

v = \frac{c}{n}

where:
v is the speed of light in the material
c is the speed of light in a vacuum
n is the refractive index of the material

doesn't get much simpler than that :)
I'll be happy to check your answers.

Thanks

So it is 430/ 1.65 and 430/1.65

260.6

And 279.2

The 279.2 is great?


Is that correct?

430 isn't the speed of light in a vacuum. 430 doesn't even come into the calculation.