🛸 · 2022年10月21日

# 这题怎么判断是one-tail 还是two-tails

NO.PZ2015120604000125

The population is 6000 programmer which is supposed to be normally distributed. A sample with 100 size is drawn from the population. Based on z-statistic, 95% confidence interval of sample mean of annual salary is 32.5 (in thousands) dollars ranges from 22 (in thousands) dollars to 43 (in thousands) dollars .Calculate the standard error of mean annual salary:

A.

1.96.

B.

3.99.

C.

5.36.

C is correct.

At the 95% level of significance, the critical value is ±1.96.

So the confidence interval is $32.5±1.96 \sigma {}_{\overline{x}}$,

From the equation t 32.5 + 1.96 standard error= 43 or 32.5 - 1.96standard error ${}_{\overline{x}}$ = 22, we get ${\sigma }_{\overline{x}}=5.36.$=5.3571.