As the backmost student couldn't tell his color,
he must have seen at least one white cap, or he would have known!
The student in the middle realized this when he heard
no answer from behind. If the blind student had had a black cap the student
in the middle could be sure his was white. But the blind student had a
white cap so he couldn't answer either.
As the blind student realized that neither of his fellow
students could answer he concluded that his own cap must be white and answered
that!
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Last updated: 01-10-30 by Ingvar
Jönsson