Ninety percent of light incident on a certain piece of glass passes through it. How much light passes through two pieces of this glass?
A) 81%
B) 90%
C) 85%
D) 89%
E) 80%

Question

Quizplus · Accepted Answer

When light passes through the first piece of glass, 90% of it is transmitted. When the transmitted light encounters the second piece, 90% of that light is again transmitted. Therefore, the total transmission is 0.9 * 0.9 = 0.81 or 81%.

Ninety Percent of Light Incident on a Certain Piece of Glass