1。一份报纸说“超过一半的医生说会在3年内退休”，是一个医疗机构做的调查，发出了19，000封信，收到了2000封完整的回信，你怎么认为开头的那句话？（从统计学的角度来看，就是样本什么什么的）
2。 一个大学共录取了6500名学生，3000名是半天part-time的，3500名是全天full-time的， （后面的我就用英文了，翻译太麻烦了不知道怎么翻译合适，不好意思）Assume that the college can provide you with a list of students that is sorted all full-time students are listed first, followed by the part-time students. a) Select a stratified random sample that used full-time and part-time students as the two strata and that includes 10 students from each stratum. Describe the procedure you used to select the sample, and identify the students included in your sample by placement on the sorted list.
b) Does every student at this community college have the same chance of being selected for inclusion in the sample? Explain.

谢谢了，我刚开始学，很多不明白的地方。