NO.PZ2022071202000060
问题如下：
Question An analyst determines that approximately 99% of the observations of daily sales for a company are within the interval from $230,000 to $480,000 and that daily sales for the company are normally distributed. If approximately 99% of all the observations fall in the interval μ ± 3σ, then using the approximate z-value rather than the precise table, the standard deviation of daily sales for the company is closest to:选项：
A.$41,667.00 B.$62,500.00 C.$83,333.00解释：
Solution
A is correct. Given that sales are normally distributed, the mean is centered in the interval.
Mean = ($230,000 + $480,000)/2 = $355,000
99 percent of observations under a normal distribution will be approximately plus/minus three standard deviations. Then, use the following formula:
Z = (X - μ)/σ
or, by rearranging:
σ = (X - μ)/Z
where
Z = 3
X = $480,000
μ = $355,000
Thus, ($480,000 - $355,000)/3.0 = $41,667.
