Yahoo 知識+ 將於 2021 年 5 月 4 日 (美國東岸時間) 停止服務。從 2021 年 4 月 20 日 (美國東岸時間) 起,Yahoo 知識+ 網站將轉為僅限瀏覽模式。其他 Yahoo 資產或服務,或你的 Yahoo 帳戶將不會有任何變更。你可以在此服務中心網頁進一步了解 Yahoo 知識+ 停止服務的事宜,以及了解如何下載你的資料。

CLP 發問於 科學及數學數學 · 8 年前

Help!!Noraml Distribution

1. The statistics department at a local university notes that the English scores of

high school seniors applying admission into their program are normally distributed with mean 610 marks and standard deviation 50 marks.

(a) If 15%students gets grade A, 25% students gets grade B, 40% students gets

grade C, and the 20% gets grade D. What are the minimium criteria to get A and B respectively?

(b)what are the mean and standard deviation of the sample means, for each

sample consisting the English scores of 40 randomly selected applicants?

(c)What is the probability that the mean English score in a simple random sample of 40 applicants is above 625 marks?

Need help!!!

1 個解答

評分
  • ?
    Lv 7
    8 年前
    最愛解答

    1(a) P(X >= a) = 0.15P[(X - 610)/50 >= (a - 610)/50] = 0.15(a - 610)/50 = 1.0364a = 661.82P(X >= b) = 0.4P[(X - 610)/50 >= (b - 610)/50] = 0.4(b - 610)/50 = 0.2533b = 622.665So, the minimium criteria to get A and B are 661.82 and 622.665 marks respectively(b) Mean = 610 and standard deviation = 50/√40 = 7.9057(c) P(X > 625) = P[(X - 625)/7.9057 > (625 - 610)/7.9057] = P(Z > 1.89736519)=0.02889

還有問題嗎?立即提問即可得到解答。