题目
For a sample of the past 30 monthly stock returns for McCreary, Inc., the mean return is 4% and the sample standard deviation is 20%. Since the population variance is unknown, the Standard error of the sample is estimated to be: S_X=(20%)/√30=3.65% The related t-table values are (t_(i，j)denotes the (100-j)^th percentile of t-distribution value with i degrees of freedom):
「huixue_img/importSubject/1564169387739582464.png」What is the 95% confidence interval for the mean monthly return?
选项
A.[-3.453%,11.453%]
B.[-2.201%,10.201%]
C.[-2.194%,10.194%]
D.[-3.464%,11.464%]
答案
D
解析
Here the t-reliability factor is used since the population variance is unknown. Since there are 30 observations, the degrees of freedom are 30-1=29. The t-test is a two-tailed test. So the correct critical t-value is「huixue_img/importSubject/1564169387781525504.png」, thus the 95% confidence interval for the mean return is: [4%-2.045×3.65%,4% 2.045×3.65%] = [- 3.464%,11.464%]