Statistic!! 跪求高手解答

A common problem in statistics is to obtain information about the mean of a population. If the population is small, we can ordinarily determine mean exactly by first taking a census and then computing mean from the population data. In most cases, however, because the population under consideration will be large, taking a census will be impractical, impossible, or extremely expensive. Usually we can obtain: 1.) Using a sample mean to estimate a population mean;2.) Illustrate confidence intervals;3.) Interpreting confidence intervals.The confidence level of a confidence interval for a population mean signifies the confidence of the estimate; this is, expresses the confidence we have that mean actually lies in the confidence interval. The length of the confidence interval indicates the precision of the estimate. Long confidence intervals indicate poor precision, whereas short confidence intervals indicate good precision.

咁......啫係要幾多個數據先為之準確~還有的是~有中文嗎??