搜搜考试网一道英语概率的题,非常急!
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一道英语概率的题,非常急!
It has been found that 72.3% of all unsolicited mail delivered to households goes unread.Over the course of a month,a household receives 80 pieces of unsolicited mail.
1、What is the mean of the sample proportion of pieces of unread mail?
2、What is the variance of the sample proportion?
3、What is the standard error of the sample proportion?
4、What is the probability that the sample proportion is greater than 0.
It has been found that 72.3% of all unsolicited mail delivered to households goes unread.Over the course of a month,a household receives 80 pieces of unsolicited mail.
1、What is the mean of the sample proportion of pieces of unread mail?
2、What is the variance of the sample proportion?
3、What is the standard error of the sample proportion?
4、What is the probability that the sample proportion is greater than 0.
p = 72.3% = 0.723,n = 80
mean of the sample proportion = np = 0.723*80 = 57.84
variance s^2 = p(1-p)/(n-1) = (0.723)*(1-0.723)/(79) ≈ 0.002535
standard error s = √0.00254 ≈ 0.05040
p(p>0.7) = p(z>(0.7-p)/s) ≈ p(z>-0.46) = 0.6772
mean of the sample proportion = np = 0.723*80 = 57.84
variance s^2 = p(1-p)/(n-1) = (0.723)*(1-0.723)/(79) ≈ 0.002535
standard error s = √0.00254 ≈ 0.05040
p(p>0.7) = p(z>(0.7-p)/s) ≈ p(z>-0.46) = 0.6772