統計學!求求你們幫幫我

The mean of the sample of 100 viewers follows a normal distribution of:

μ = 0.55

σ = √(0.45 x 0.55/100) = 0.0497

Now 0.5 has a z-score of:

z = (0.5 - 0.55)/0.0497 = 1.005

So the required probability is:

P(z < 1.005) = 0.1574

2012-05-10 13:47:23 補充：
Thanks to the comment of 自由自在, if using 0.495, then:

Now 0.495 has a z-score of:

z = (0.495 - 0.55)/0.0497 = -1.106

So the required probability is:

P(z < -1.106) = 0.1345

so 自由自在 ( 知識長 ) you mean that usually use normal distribution are not correct???

002 以binomial distribution計算,數值當然正確,但一般情況下,以normal distribution估算,計法比較簡單,所以001的答法是比較多被採用的.然而001及002的計算結果相差很大,因為作normal distribution估算時,要加上correction factor,即不以0.5估算,而是用0.495估算,才有較滿意結果...

http://s1152.photobucket.com/albums/p489/minglamchoi/statistic.jpg

圖片參考：http://imgcld.yimg.com/8/n/HA08217754/o/701205080092713873404610.jpg