Miss Sullivan taught Helen many things -- to read and write, and even to use a typewriter.
VOA: special.2009.11.08
Well, the mean is always .2 no matter how many policies you write, so it's going to be--we're going to have a normal distribution centered on .2.
不论你签了多少份保单,均值永远是0.2,所以这就是一个关于x=0.2对称的,正态分布
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