请问老师这个题怎么做

请问semiannual payment but quarterly compounding 这个题怎么做？

这题是怎么做出来的 In a metal fabrication process, metal rods are produced that have an average length of 20.5 metres with a standard deviation of 2.3 metres. A quality control specialist collects a random sample of 30 rods and measures their lengths. 问题Suppose the resulting sample mean is 19.5 metres. Do you think that this sample result is unusually small? Explain. 答案：We have a random sample of metal rods drawn from a much larger population. A sample mean of only 19.5 metres is about 2.38 standard deviations below what we expect. The sample mean of 19.5 metres is unusually small.

In a metal fabrication process, metal rods are produced that have an average length of 20.5 metres with a standard deviation of 2.3 metres. A quality control specialist collects a random sample of 30 rods and measures their lengths. 问题：Suppose the resulting sample mean is 19.5 metres. Do you think that this sample result is unusually small? Explain. 答案：We have a random sample of metal rods drawn from a much larger population. A sample mean of only 19.5 metres is about 2.38 standard deviations below what we expect. The sample mean of 19.5 metres is unusually small. 老师我想请问这个题的答案怎么出来的，2.38这个数字怎么来的

这里的correlation是指的线性相关吗？？求解

这里的correlation是指的线性相关吗？？求解

这里的correlation是指的线性相关吗？

这里的correlation是指的线性相关吗？

这里的correlation是指的线性相关吗？

这里的correlation是指的线性相关吗？