In a college, 20% of the students have a part-time job
a) Find the probability that in a random sample of 20 students
i. exactly 4 of them has part-time job
ii. at least 2 of them has part time job.
b) Among 100 students, how many would you expect to have a part0time job?
c) How large must a random sample be if the probability that it contains at least one student with a part-time job is to be greater than 0.95
I cant find the ans out../__\\
probability....question
2007-11-17 8:07 am
回答 (1)
2007-11-17 8:32 am
✔ 最佳答案
ANSWERThe no of students have a part-time job ~ BIN(20,0.2)
(a)
(i)
p(4)=20C4(0.2)^4(0.8)^16=0.2182
(ii)
the required probability
=1-p(0)-p(1)
=1-0.8^20-20(0.2)(0.8)^19
=0.9308
(b)
here n=100, p=0.2
E(x)=np=20
I expect 20 students have a part time job
(c)
Want P(x>=1)>=0.95
Since the probability that the sample contains at least one student with a part-time job
=1-p(0)
=1-(0.8)^n
So let 1-(0.8)^n>=0.95
(0.8)^n<=0.05
n>=13.4
So n=14
收錄日期: 2021-04-25 16:53:34
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