问题
单项选择题
Construct a 90 percent confidence interval for the starting salaries of 100 recently hired employees with average starting salaries of $ 50000 and a standard deviation of $ 3000 assuming the population has a normal distribution.（）
A. 50000±1.65 (3000);
B. 50000±1.65 (300).
C. 30000±1.65 (5000).
答案
参考答案：A
解析：
90% confidence interval is X±1.65s=50000±1.65×3000 =$45050 to $54950