英语的统计学问题,有关标准差、平均值
 A group of 13 students is studying in Istanbul,Turkey,for five weeks.As part of their study of the local 
economy,they each purchased an Oriental rug and arranged for its shipment back to the United States.The
shipping time,in days,For each rug was 
31     31     42     39      42     43      34    
30     28      36     37     35     40  
Estimate the percentage of days that are within two standard deviations of the Mean.Is it likely to take 2 
months for a delivery? 





Estimate the percentage of days that are within two standard deviations of the Mean.

请写出具体的计算步骤