[問題] 94北科統計2題

看板Grad-ProbAsk作者s911125 (江小LO)時間15年前 (2009/03/24 20:52)推噓1(1推 0噓 1→)

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1.a computer,in adding numbers,rounds each number off to the nearest integer. suppose that all rounding errors are independent and unformly distributed over (-0.5,0.5).if 1500 numbers are added,what is the probability that the magnitude of the total error exceeds 15 ? A. 0.1802 b. 0.3132 c. 0.0451 d. 0.2842 我的算法是這樣 X~U(-0.5,0.5) E(X)=0 V(X)=1/12 Y=X(1)+X(2)+++++X(1500) E(X)=0 V(X)=1500*(1/12)=125 P(Y>15)=P(Z>(15-0)/125^1/2)=P(Z>1.34)=0.0918 請問是哪邊觀念錯了? -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 218.168.3.184

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loveliver

03/24 21:31, , 1^F

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disroxen

03/25 00:31, , 2^F

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