单选题

A sample of 100 observations drawn from a normally distributed population has a sample mean of 12 and a sample standard deviation of 4. Using the extract from the z-distribution given below, find the 95% confidence interval for the population mean.

A、 7.840 to 27.683
B、 11.216to 12.784
C、 11.340to 12.660

【正确答案】 B

【答案解析】

The 95% confidence interval uses z0 .025 as the reliability factor. The cumulative probability value closest to 0.975 provides the appropriate value of z0 .025 which is z0 .025 = 1.96. The confidence interval is formed as:

In this problem,12 ±1.96 × (4 /