投擲一對公正骰子的隨機實驗,令隨機變數X表骰子出現的點數和,則E(X) =
(1) ,Var(X) = (2) 。
若二隨機變數X、Y 的joint p.d.f.為f (x, y) = x + y,0 < x < 1,0 < y < 1,則
共變異數Cov(X,Y ) = (3) ,相關係數ρ (X,Y ) = (4) 。
已知中山財管系同學課堂外花在研習統計學之時間每天平均為102 分鐘,變異數
為36 分鐘,假設每天研讀之時間分配為常態分配,而且,一週之讀書日以6 天
計,則該系同學每週總讀書時間花在統計學之時間超過21 小時之機率為 (11) 。
The Dow Jones Industrial Average is one of the most widely quoted stock
market indexes. This index is based on a sample of 30 industrial stocks,
the so-called Dow Jones Industrials (DJI), and the average is arrived at by
adding up the prices of the 30 stocks and dividing the total by the so-called
Dow Jones divisor to obtain an average stock price adjusted for past stock
splits and stock dividends.
A similar method is used to calculate the earnings on the Dow Jones
Industrial Average: the reported quarterly earnings per share for the 30
DJI stocks are added up and the sum is divided by the DJI divisor. The
result reflects average earnings per share adjusted for the cumulative
effect of stock splits and stock dividends. The following table gives the
quarterly earnings on DJI average for the period 1975-81.
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