问题
单项选择题
The minimum proportion of observations falling within 2 standard deviations of the mean is closest to:（）
A. 95%.
B. 75%.
C. 68%.
答案
参考答案：B
解析：
According to Chebyshev’s inequality, the proportion of the observations within 2, which is k, standard deviations of the mean is at least 1-(1/k)2=1-(1/22)=0.75 or 75%.