我在解答伍德里奇的《计量经济学导论》中第二章计算机习题的第一题时遇到了困难。
在输入下列命令后：
. infile prate mrate using "D:\My Documents\学期资料\计量经济学\401K.raw",clear
(6136 observations read)

. de
Contains data
obs: 6,136
vars: 2
size: 73,632 (99.3% of memory free)
-------------------------------------------------------------------------------
storagedisplay value
variable name type format label variable label
-------------------------------------------------------------------------------
prate float%9.0g
mrate float%9.0g
-------------------------------------------------------------------------------
Sorted by:
Note:dataset has changed since last saved

. sum prate mrate
Variable | Obs Mean Std. Dev. Min Max
-------------+--------------------------------------------------------
prate | 6136 363.8156 2383.93 0 58811
mrate | 6136 1300.818 6379.993 .01 140000
显示prate的平均值是363.8156，但是答案说应该是87.36。请问这是怎么回事啊？