单选题

An analysis determined that approximately 99 percent of the observations of daily sales for a company were within the interval from $250000 to $580000 and that daily sales for the company were normally distributed. The mean daily sales and standard deviation of daily sales, respectively, for the company were closest to（）。

【正确答案】 B

【答案解析】

Given that sales are normally distributed, the mean is centered in the interval mean=($250000+$580000)/2=$415000.
An interval including 99% of the observations extends three standard deviations either side of the mean. The standard deviation of daily sales= ($415000-$250000)/3=$55000.