Probability 概率
概念
维基百科 Probability is the branch of mathematics concerning numerical descriptions of how likely an event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and 1, where, roughly speaking, 0 indicates impossibility of the event and 1 indicates certainty. The higher the probability of an event, the more likely it is that the event will occur. A simple example is the tossing of a fair (unbiased) coin. Since the coin is fair, the two outcomes (“heads” and “tails”) are both equally probable; the probability of “heads” equals the probability of “tails”; and since no other outcomes are possible, the probability of either “heads” or “tails” is 1/2 (which could also be written as 0.5 or 50%). 概率,旧称几率,又称机率、机会率或或然率,是数学概率论的基本概念,是一个在 0 到 1 之间的实数,是对随机事件发生之可能性的度量。
离散型变量取某个值
连续型变量取某个值
例如,从所有自然数中任取一个数,问这个数等于 5 的概率是多少?从所有的自然数中取一个,当然是有可能取到 5 的,但是自然数有无穷多个,因此取到 5 的概率是
又如扔飞镖,虽然是有可能落在靶心的,但其概率也是 0(不考虑熟练程度等其他因素),因为靶盘上有无数个点,每个点的概率是一样的,因此落在某一个具体的点上的概率为
根据前面的例子可知:在连续型变量中:概率为 0 的事件是有可能发生的,概率为 1 的事件不一定必然发生。
#待整理笔记