To a fish, the 4.00m thick aquarium walls appear only 3.50m thick.
how do i calculate this?
2 Answers

use this:
apparent thickness/thickness = speed of light in water/speed of light in glass.
speed of light in water/speed of light in glass = 1.33/1.5
so apparent thickness = thickness*1.33/1.5 = 4*1.33/1.5 = 3.54m

your asked to solve for n. 4.00mm/3.50mm == nmaterial=?/nwater=1.33 ; thus nmat=1.52