碰到一个notes上的问题，希望大家能指点和解惑：
The 95% confidence interval of the sample mean of employee age for a major co. is 19y to 44y based on a Z-statistic.The population of employees is more than 5000 and the sample size of this test is 100.Assuming the population is normally distributed, the standard error of mean employee age is closest to:A)1.96；B)2.58；C)6.38；D）12.5。
我怎么算出来是0.638没有答案啊。
I know how i got a mistake
the standard error of mean is to calculate the sample standard deviation based on known population variance.
What I took the (44-19)/2/1.96 divided by the root of sample size is gild the lily.
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