Answer:
The ratio of the speed of light in glass to the speed of light in a vacuum is 2:3.
Step-by-step explanation:
Given that,
Speed of light in vacuum = 186000 miles/sec
Speed of light in glass = 124000 miles/sec
We need to calculate the ratio of the speed of light in glass to the speed of light in a vacuum
The ratio of speed of light in glass to the vacuum

Where,
= speed of light in vacuum
= speed of light in vacuum

Hence, The ratio of the speed of light in glass to the speed of light in a vacuum is 2:3.