又想起来一个数学的比较变态。说normal distribution. 83% lies within 1 standard deviation of the mean, 96% lies within 2 standard deviation of the mean. In 2000 data points, normally distributed, the mean is 18.6, with standard deviation 6, what percentage of the data lies beteween 6.6 and 12.6.
答案是 (96%-83%)/2=6.5%
数字可能不完全对,但是是这样算的