收到两个难题，求助解决
Which of the following describes the 95% confidence interval of a 20% absentee rate in a department with 30 people?
(A) 6% to 34%
(B) 8% to 32%
(C) 13% to 27%
(D) 17% to 23%
When σ = 10, what sample size is needed to specify a 95% confidence interval of +/_ 3 units from the mean?
(A) 7
(B) 11
(C) 32
(D) 43
(A) 6% to 34%
(B) 8% to 32%
(C) 13% to 27%
(D) 17% to 23%
When σ = 10, what sample size is needed to specify a 95% confidence interval of +/_ 3 units from the mean?
(A) 7
(B) 11
(C) 32
(D) 43
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szbb (威望:2) (湖北 )
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2。答案为D。 具体算法为： S＝σ / sqrt(n) 1.96*S =3
sqrt(n)=(1.96*σ/3) =6.5 n=43