In 1951, the Nobel prize-winning physicist Albert Einstein was teaching at Princeton University. He had just administered an examination to an advanced class of physics students and was on his way back to his office. His teaching assistant was walking with him, carrying the completed exam papers.
The assistant, a little shy in the presence of the greatest physicist of the twentieth century, asked him, “Dr. Einstein, wasn’t that exam that you gave this class of physics students the same exam that you gave to this same class last year?”
Dr. Einstein thought for a moment and then said, “Yes, it was the same exam.”
The teaching assistant then asked hesitantly, “But Dr. Einstein, how could you give the
same exam to the same class, two years in a row?”
Einstein’s answer was classic. He said, “Well, the answers have changed.”