3. Samantha was a student at University of Wisconsin - Stout majoring in Accounting. In the summer after her sophomore year she got an intern job at the First National Bank. As her boss, Brad, assumed that she must have taken statistics course in the business school, he asked Samantha to give him a 95% interval estimate of the average amount of money their customers opened a certificate deposit with the bank. Samantha randomly selected 5 from all the certificate deposits currently valid with them and found the principals were $5,800, $6,000, $5,300, $8,100, and 7,300. Samantha gave an interval estimate of between $5,292 to $7,708. Was she correct? If not, what do you think a correct interval would be? (16 %)

     我是珊曼莎，主修會計，現在第一銀行實習

      我是布萊德，珊曼莎的上司，要考考珊曼莎的統計學實力

考題 : 估計出存戶平均存款金額95%的信賴區間

    珊曼莎隨機抽了5個存戶
 5,800  ,  6,000 ,  5,300,    8,100 , 7,300  (假設存款金額呈常態)

   樣本數 n = 5，自由度d.f.=4

      t分配表

查表得到 t 值

95%的信賴區間介於 5060.18 到  7939.82

珊曼莎的答案是介於 5,292  到    7,708 (不對!區間沒有這麼窄)