作者ebenezer (我要打十個)
看板Grad-ProbAsk
標題[問題] 97年北商國際商務所統計學考題
時間Sun Mar 22 03:03:05 2009
題目:In a surveys,75% of the voters supports a particular referendum.If 60
voters are chosen,and x is the number of voters that supports this
referedum,what is the variance of x?
(A)3.3541(B)3.75(C)6.7082(D)33.75(E)11.25
這題我的想法是:VAR(X)=E(X^2)-(E(X))^2
=60X60X0.75-(60X0.75)^2
=675
可是答案沒有這個選項!我在想是不是我哪個觀念錯誤了,麻煩版上的高手給予指導
感恩!
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◆ From: 218.166.50.60
1F：→ kyht:X~B(60,0.75) Var(X)=60x0.75x0.25=11.25 03/22 19:08