統計學 討論 binominal.. 
95208056@(95208056 2008-10-19 23:12:02
1樓
A manufacture of floor wax has developed two new brands, A and B, which sge wishes to subject to homeowners' evaluation to determine
which of the two is superior. Both waxes, A and B, are applied to floor surfaces in each of 15 homes. Assume that there is actually no difference
in the quality of the brands. What is the probability that ten or more homeowners would state a perference for

a. brand A?                                                                            ans:     0.151
b. either brand A or brand B?                                             ans:    0.302

這題我我考慮brandA=1/2 , brandB=1/2  或是, brandA= 1/3 , brandB=1/3, others = 1/3 這兩種情形帶入的答案都不對 ˊˋ..
不知道我是不是沒考慮到其他什麼




另ㄧ題..

Of the volunteers donating blood in a clinic, 80% have the Rh factor present in their blood.
What is the smallest number of volunteers who must be selected if we want to be at least 90% certain that we obtain at least 5 donors with Rh factor?

ans:8

我想請問,這題除了ㄧ個ㄧ個數字套入,還有其他解法嗎?
95354008@(季圓-統計學輔導員 2008-10-22 16:09:04
2樓
同學你好,

第一題題目中有提到Assume that there is actually no difference in the quality of the brands,所以是用1/2代。而代入1/2後可以binomial機率分配公式求得喜歡brand A的機率,即binomial分配      n=15     求P(X>=10)的機率,答案是進位後是0.151沒錯。

同理brand B的發生機率因為也是0.151,且兩事件為互斥,因此A或B發生的機率為0.151+0.151=0.302。


而第二題目前我想到的方法也是直接代,如果有二項表可查的話其實不會太慢只要加總就好,希望有其他助教有更快的發法可以提出來。

有問題歡迎在發問喔^^
95208056@(95208056 2008-10-24 01:51:55
3樓
謝謝!
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