作者oppo2121 (随风)
看板Grad-ProbAsk
标题Re: [问题] 94北科统计2题
时间Thu Mar 26 00:48:06 2009
※ 引述《s911125 (江小LO)》之铭言：
: 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
: 我的算法是这样 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
: 请问是哪边观念错了?
total error
所以误差无正负....机率取双尾
所以最後算的答案要x2
P(|Z|>1.34)=0.0918x2=接近0.1802
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1F：推 s911125:感谢你~ 03/26 12:37