第六童引言 Introduction) Problem of buffon's needle. If a needle of length l is dropped at random on the middle of a horizontal surface ruled with parallel lines a distance dl apart, what is the probability that the needle will cross one of the lines? I sine d第六章 引言(Introduction) Problem of Buffon’s needle: If a needle of length l is dropped at random on the middle of a horizontal surface ruled with parallel lines a distance d>l apart, what is the probability that the needle will cross one of the lines?