单选题
An analyst determined that approximately 99 percent of the observations of daily sales for a company were within the interval from $230000 to $480000 and that daily sales for the company were normally distributed. The standard deviation of daily sales for the company was closest to:
【正确答案】
C
【答案解析】[解析] 由于观测值服从正态分布，从而其平均值位于区间中央，亦即平均值
=(230000+480000)/2=355000美元。
99%的置信区间为[
-2.58σ，
=(230000+480000)/2=355000美元。
99%的置信区间为[
-2.58σ，