1. The problem statement, all variables and given/known data A sheet of plastic, n= 1.5, 25 mm thick is used in a bank teller's window. A ray of light strikes the sheet at an angle of 45 degrees. The ray leaves the sheet at 45 degrees, but at a different location. Use a ray diagram to find the distance between the ray that leaves and the one that would have left if the plastic were not there. 2. Relevant equations I understand the entirety of this solution: http://answers.yahoo.com/question/index?qid=20090410213448AAiL3zm However, I don't understand the wording of the problem above, which is from my textbook. The yahoo answers solution seems to contradict what the problem says-- and that is that the ray of light leaves at a 45 degree angle if the plastic IS there. However, the link seems to imply that such would occur if the plastic was NOT there. I agree that if the plastic was not there, the light would just keep going at a 45 degree from the normal. So what does this problem mean? 3. The attempt at a solution I pretty much attempted it the same way the yahoo answers attempts it. ^ I'm having a hard time understanding it because of the way the problem is worded. Thank you so much in advance!